Typo in extensions.rst: Link to CFFI did not work.

Author: hamogu

source/extensions.rst

@@ -156,7 +156,7 @@ wrapper modules up to date.
   modules. It still involves wrapping the interfaces by hand, however, so
   may not be a good choice for wrapping large APIs.
 
-* `cffi <cffi.readthedocs.org/>`__ is a project created by some of the PyPy
+* `cffi <http://cffi.readthedocs.org/>`__ is a project created by some of the PyPy
   developers to make it straightforward for developers that already know
   both Python and C to expose their C modules to Python applications. It
   also makes it relatively straightforward to wrap a C module based on its