Update 'requests' lib to v2.0.

third_party/requests/exceptions.py

Index: third_party/requests/exceptions.py
diff --git a/third_party/requests/exceptions.py b/third_party/requests/exceptions.py
index c0588f6aedec47f18553f186c742afba5a256065..22207e35394902043453133574a844db630214a5 100644
--- a/third_party/requests/exceptions.py
+++ b/third_party/requests/exceptions.py
@@ -9,7 +9,7 @@ This module contains the set of Requests' exceptions.
 """
 
 
-class RequestException(RuntimeError):
+class RequestException(IOError):
     """There was an ambiguous exception that occurred while handling your
     request."""
 
@@ -53,3 +53,7 @@ class InvalidSchema(RequestException, ValueError):
 
 class InvalidURL(RequestException, ValueError):
     """ The URL provided was somehow invalid. """
+
+
+class ChunkedEncodingError(RequestException):
+    """The server declared chunked encoding but sent an invalid chunk."""