add missing period (cherry picked from commit c7b1bff)

Steve Piercy

2015-11-04 bb15edf27be2b2d525d25b43a2bdae0294328459

add missing period
(cherry picked from commit c7b1bff)

 docs/narr/introspector.rst

@@ -136,7 +136,7 @@
  ``predicates``

    The predicate objects created as the result of passing predicate arguments
    to ``add_subscriber``
    to ``add_subscriber``.

  ``derived_predicates``