README: stop claiming py2.5 compatibility.

Author: warner

README.md

@@ -20,7 +20,7 @@ other curves are included, but it would not be too hard to add more.
 
 ## Dependencies
 
-This library uses only Python. It requires python2.5 or later versions of the
+This library uses only Python. It requires python2.6 or later versions of the
 python2.x series. It is also compatible with python3.2 and 3.3.
 
 To run the OpenSSL compatibility tests, the 'openssl' tool must be on your