Update requirements.txt (#66)

Pinned to version `2.17.7`, until we can update the code to not depend on `epylint`.  We also need to update/depreciate Python `3.7`, since versions of Pylint higher than 2.17.7 no longer support it.

Author: BethanyG

requirements.txt

@@ -1,2 +1,2 @@
-pylint >=2.17.1
-plerr ~=3.0.0
+pylint ==2.17.7
+plerr ~=3.0.0