Fixed setup.py to obtain xblock utils from edx repository

setup.py

@@ -56,7 +56,7 @@ setup(
         'ddt',
         'mock',
     ],
-    dependency_links=['http://github.com/edx-solutions/xblock-utils/tarball/master#egg=xblock-utils'],
+    dependency_links=['http://github.com/edx/xblock-utils/tarball/master#egg=xblock-utils'],
     entry_points={
         'xblock.v1': [
             'poll = poll:PollBlock',