Fix typo in the word "Continuous" (#312)

Author: Mariatta

docs/index.rst

@@ -111,7 +111,7 @@ Please feel free to file an issue on `bug tracker
 or have some suggestion for library improvement.
 
 The library uses `Travis <https://travis-ci.org/aio-libs/aiohttp_session>`_ for
-Continious Integration.
+Continuous Integration.
 
 
 Dependencies