Limit version allowed for Alabaster, fixes #1350

There is an issue with 0.7.5, we will blacklist the version here. The range was
replicated from Sphinx, but should likely be pinned to a specific version we
support in the future. This will require defining supported packages and a
procedure for keeping pinned dependencies up to date.

Author: agjohnson

readthedocs/projects/tasks.py

@@ -339,6 +339,7 @@ def setup_environment(version):
         'pillow==2.6.1',
         'readthedocs-sphinx-ext==0.5.4',
         'sphinx-rtd-theme==0.1.8',
+        'alabaster>=0.7,<0.8,!=0.7.5',
         'recommonmark==0.1.1',
     ])