Christian Clauss 0f09530707 dijkstra.py: Use r"strings" to fix two pylint warnings ()
```
=============================== warnings summary ===============================
graphs/dijkstra.py:81
  /home/travis/build/TheAlgorithms/Python/graphs/dijkstra.py:81: DeprecationWarning: invalid escape sequence \ 
    """
graphs/dijkstra.py:97
  /home/travis/build/TheAlgorithms/Python/graphs/dijkstra.py:97: DeprecationWarning: invalid escape sequence \ 
    """
-- Docs: https://docs.pytest.org/en/latest/warnings.html
=================== 126 passed, 7 warnings in 19.35 seconds ====================
```
2019-07-21 00:31:08 +08:00
..
2019-05-26 21:56:10 +05:30
2019-05-26 21:56:10 +05:30