fix indentation

Travis build is failing:

    ======================================================================
    ERROR: Failure: IndentationError (unindent does not match any outer indentation level (gevent_zmq.py, line 142))
    ----------------------------------------------------------------------
    Traceback (most recent call last):
      File "/home/travis/virtualenv/python2.7/local/lib/python2.7/site-packages/nose/loader.py", line 413, in loadTestsFromName
        addr.filename, addr.module)
      File "/home/travis/virtualenv/python2.7/local/lib/python2.7/site-packages/nose/importer.py", line 47, in importFromPath
        return self.importFromDir(dir_path, fqname)
      File "/home/travis/virtualenv/python2.7/local/lib/python2.7/site-packages/nose/importer.py", line 94, in importFromDir
        mod = load_module(part_fqname, fh, filename, desc)
      File "/home/travis/build/dotcloud/zerorpc-python/zerorpc/__init__.py", line 27, in <module>
        from .context import *
      File "/home/travis/build/dotcloud/zerorpc-python/zerorpc/context.py", line 29, in <module>
        import gevent_zmq as zmq
      File "/home/travis/build/dotcloud/zerorpc-python/zerorpc/gevent_zmq.py", line 142
        break
            ^
    IndentationError: unindent does not match any outer indentation level

Wrong indentation, not sure where this was introduced...