Auto-format all files using yapf and pre-commit (#1173)

Automatic fixes produced by yapf formatting using `--style=google`, as
well as common pre-commit checks such as trailing whitespace removal,
double quote fixer, and newlines at the end of a file.

src/gam.py

@@ -7,5 +7,5 @@ import sys
 from gam.__main__ import main
 
 # Run from command line
-if __name__ == "__main__":
-    main(sys.argv)
+if __name__ == '__main__':
+    main(sys.argv)