Add .pyre directory for Pyre type checker

Pyre is a new type-checker for Python developed by facebook in May 2018.
https://pyre-check.org/

It makes .pyre directory for storing result or cache for type checking.
This directory is environment dependent. So it should be ignored from Git.

Python.gitignore

@@ -109,3 +109,6 @@ venv.bak/
 .mypy_cache/
 .dmypy.json
 dmypy.json
+
+# Pyre type checker
+.pyre/