Add stub for cryptography.hazmat.primitives.serialization (#851)

This makes the stubs for cryptoraphy less incompelete. Created using
stubgen. I don't know what the types are.

third_party/2/cryptography/hazmat/primitives/serialization.pyi

@@ -0,0 +1,32 @@
+# Stubs for cryptography.hazmat.primitives.serialization (Python 2)
+#
+# NOTE: This dynamically typed stub was automatically generated by stubgen.
+
+from typing import Any
+from enum import Enum
+
+def load_pem_private_key(data, password, backend): ...
+def load_pem_public_key(data, backend): ...
+def load_der_private_key(data, password, backend): ...
+def load_der_public_key(data, backend): ...
+def load_ssh_public_key(data, backend): ...
+
+class Encoding(Enum):
+    PEM = ...  # type: str
+    DER = ...  # type: str
+
+class PrivateFormat(Enum):
+    PKCS8 = ...  # type: str
+    TraditionalOpenSSL = ...  # type: str
+
+class PublicFormat(Enum):
+    SubjectPublicKeyInfo = ...  # type: str
+    PKCS1 = ...  # type: str
+
+class KeySerializationEncryption: ...
+
+class BestAvailableEncryption:
+    password = ...  # type: Any
+    def __init__(self, password) -> None: ...
+
+class NoEncryption: ...