Ignore .pytype/ directory (#3301)

pytype is a static type analyzer for Python code;
it generates files of inferred type information,
located by default in .pytype/pyi.

Python.gitignore

@@ -127,3 +127,6 @@ dmypy.json
 
 # Pyre type checker
 .pyre/
+
+# pytype static type analyzer
+.pytype/