Update bitbucket.py

Author: rjlardizabal

atlassian/bitbucket.py

@@ -1158,4 +1158,4 @@ def upload_file(self, project, repository, content, message, branch, filename):
             project=project,
             repository=repository,
             filename=filename)
-        return self.put(url, data=data)
+        return self.put(url, files=data)