Correct spelling of "Bitbucket"

Author: bittner

README.txt

@@ -73,7 +73,7 @@ Join the `virtualenvwrapper Google Group
 <http://groups.google.com/group/virtualenvwrapper/>`__ to discuss
 issues and features.  
 
-Report bugs via the `bug tracker on BitBucket
+Report bugs via the `bug tracker on Bitbucket
 <https://bitbucket.org/dhellmann/virtualenvwrapper/issues>`__.
 
 Shell Aliases