Fix gl version using strings.

This was causing 'is_legacy' and 'is_core' to fail
as they expected ints.

Author: adamlwgriffiths

pygly/gl.py

@@ -59,7 +59,7 @@ def _extract_version(version):
     # there can be a 3rd version
     # split full stops and spaces and take the first 2 results
     versions = re.split( r'[\.\s\-]', version )
-    return versions[ 0 ], versions[ 1 ]
+    return int(versions[0]), int(versions[1])
 
 def gl_version():
     """Returns the current OpenGL version string as specified by the