Fix typehints in project_euler/problem01 (#2891)

Squashed commit of the following:

commit 6801d073b31bf702814861cd3b07b634ca295bfa
Author: Archaengel <god11341258@gmail.com>
Date:   Mon Oct 5 16:40:10 2020 -0700

    Fix typehints in project_euler/problem01

commit 29afc3af114abd1b99dc3f7c8fc99128229db131
Author: Archaengel <god11341258@gmail.com>
Date:   Mon Oct 5 15:06:34 2020 -0700

    Add typehints and default argument for project_euler/problem_01

project_euler/problem_01/sol1.py

@@ -6,7 +6,7 @@ Find the sum of all the multiples of 3 or 5 below N.
 """
 
 
-def solution(n):
+def solution(n: int = 1000) -> int:
     """Returns the sum of all the multiples of 3 or 5 below n.
 
     >>> solution(3)

project_euler/problem_01/sol2.py

@@ -6,7 +6,7 @@ Find the sum of all the multiples of 3 or 5 below N.
 """
 
 
-def solution(n):
+def solution(n: int = 1000) -> int:
     """Returns the sum of all the multiples of 3 or 5 below n.
 
     >>> solution(3)

project_euler/problem_01/sol3.py

@@ -6,7 +6,7 @@ Find the sum of all the multiples of 3 or 5 below N.
 """
 
 
-def solution(n):
+def solution(n: int = 1000) -> int:
     """
     This solution is based on the pattern that the successive numbers in the
     series follow: 0+3,+2,+1,+3,+1,+2,+3.

project_euler/problem_01/sol4.py

@@ -6,7 +6,7 @@ Find the sum of all the multiples of 3 or 5 below N.
 """
 
 
-def solution(n):
+def solution(n: int = 1000) -> int:
     """Returns the sum of all the multiples of 3 or 5 below n.
 
     >>> solution(3)

project_euler/problem_01/sol5.py

@@ -8,7 +8,7 @@ Find the sum of all the multiples of 3 or 5 below N.
 """A straightforward pythonic solution using list comprehension"""
 
 
-def solution(n):
+def solution(n: int = 1000) -> int:
     """Returns the sum of all the multiples of 3 or 5 below n.
 
     >>> solution(3)

project_euler/problem_01/sol6.py

@@ -6,7 +6,7 @@ Find the sum of all the multiples of 3 or 5 below N.
 """
 
 
-def solution(n):
+def solution(n: int = 1000) -> int:
     """Returns the sum of all the multiples of 3 or 5 below n.
 
     >>> solution(3)

project_euler/problem_01/sol7.py

@@ -6,7 +6,7 @@ Find the sum of all the multiples of 3 or 5 below N.
 """
 
 
-def solution(n):
+def solution(n: int = 1000) -> int:
     """Returns the sum of all the multiples of 3 or 5 below n.
 
     >>> solution(3)