Replace Travis CI mentions with GitHub actions (#5751)

CONTRIBUTING.md

@@ -23,7 +23,7 @@ __Improving comments__ and __writing proper tests__ are also highly welcome.
 
 We appreciate any contribution, from fixing a grammar mistake in a comment to implementing complex algorithms. Please read this section if you are contributing your work.
 
-Your contribution will be tested by our [automated testing on Travis CI](https://travis-ci.org/TheAlgorithms/Python/pull_requests) to save time and mental energy.  After you have submitted your pull request, you should see the Travis tests start to run at the bottom of your submission page.  If those tests fail, then click on the ___details___ button try to read through the Travis output to understand the failure.  If you do not understand, please leave a comment on your submission page and a community member will try to help.
+Your contribution will be tested by our [automated testing on GitHub Actions](https://github.com/TheAlgorithms/Python/actions) to save time and mental energy.  After you have submitted your pull request, you should see the GitHub Actions tests start to run at the bottom of your submission page.  If those tests fail, then click on the ___details___ button try to read through the GitHub Actions output to understand the failure.  If you do not understand, please leave a comment on your submission page and a community member will try to help.
 
 Please help us keep our issue list small by adding fixes: #{$ISSUE_NO} to the commit message of pull requests that resolve open issues. GitHub will use this tag to auto-close the issue when the PR is merged.
 
@@ -170,7 +170,7 @@ We want your work to be readable by others; therefore, we encourage you to note
 - If possible, follow the standard *within* the folder you are submitting to.
 - If you have modified/added code work, make sure the code compiles before submitting.
 - If you have modified/added documentation work, ensure your language is concise and contains no grammar errors.
-- Do not update the README.md or DIRECTORY.md file which will be periodically autogenerated by our Travis CI processes.
+- Do not update the README.md or DIRECTORY.md file which will be periodically autogenerated by our GitHub Actions processes.
 - Add a corresponding explanation to [Algorithms-Explanation](https://github.com/TheAlgorithms/Algorithms-Explanation) (Optional but recommended).
 - All submissions will be tested with [__mypy__](http://www.mypy-lang.org) so we encourage you to add [__Python type hints__](https://docs.python.org/3/library/typing.html) where it makes sense to do so.
 

project_euler/README.md

@@ -5,7 +5,7 @@ Problems are taken from https://projecteuler.net/, the Project Euler. [Problems
 Project Euler is a series of challenging mathematical/computer programming problems that require more than just mathematical
 insights to solve. Project Euler is ideal for mathematicians who are learning to code.
 
-The solutions will be checked by our [automated testing on Travis CI](https://travis-ci.com/github/TheAlgorithms/Python/pull_requests) with the help of [this script](https://github.com/TheAlgorithms/Python/blob/master/scripts/validate_solutions.py). The efficiency of your code is also checked. You can view the top 10 slowest solutions on Travis CI logs (under `slowest 10 durations`) and open a pull request to improve those solutions.
+The solutions will be checked by our [automated testing on GitHub Actions](https://github.com/TheAlgorithms/Python/actions) with the help of [this script](https://github.com/TheAlgorithms/Python/blob/master/scripts/validate_solutions.py). The efficiency of your code is also checked. You can view the top 10 slowest solutions on GitHub Actions logs (under `slowest 10 durations`) and open a pull request to improve those solutions.
 
 
 ## Solution Guidelines
@@ -28,7 +28,7 @@ Welcome to [TheAlgorithms/Python](https://github.com/TheAlgorithms/Python)! Befo
   * When the `solution` function is called without any arguments like so: `solution()`, it should return the answer to the problem.
 
 * Every function, which includes all the helper functions, if any, and the main solution function, should have `doctest` in the function docstring along with a brief statement mentioning what the function is about.
-  * There should not be a `doctest` for testing the answer as that is done by our Travis CI build using this [script](https://github.com/TheAlgorithms/Python/blob/master/scripts/validate_solutions.py). Keeping in mind the above example of [Problem 1](https://projecteuler.net/problem=1):
+  * There should not be a `doctest` for testing the answer as that is done by our GitHub Actions build using this [script](https://github.com/TheAlgorithms/Python/blob/master/scripts/validate_solutions.py). Keeping in mind the above example of [Problem 1](https://projecteuler.net/problem=1):
 
   ```python
   def solution(limit: int = 1000):

project_euler/problem_012/sol2.py

@@ -36,9 +36,8 @@ def solution():
     """Returns the value of the first triangle number to have over five hundred
     divisors.
 
-    # The code below has been commented due to slow execution affecting Travis.
-    # >>> solution()
-    # 76576500
+    >>> solution()
+    76576500
     """
     return next(i for i in triangle_number_generator() if count_divisors(i) > 500)