add (overwrite with) mypy stubs, if available

stdlib/2.7/sha.pyi

@@ -0,0 +1,12 @@
+# Stubs for Python 2.7 sha stdlib module
+
+class sha(object):
+    def update(self, arg: str) -> None: ...
+    def digest(self) -> str: ...
+    def hexdigest(self) -> str: ...
+    def copy(self) -> sha: ...
+
+def new(string: str = None) -> sha: ...
+blocksize = 0
+digest_size = 0
+