grammatical rearrangement in gp docs

Author: Darcy Meyer

docs/source/gp.rst

@@ -243,8 +243,8 @@ also need to include the additional arguments, :code:`X`, :code:`y`, and
 
 This second block produces the conditional distributions.  Notice that extra 
 arguments are required for conditionals of :math:`f1` and :math:`f2`, but not
-:math:`f`.  This is because those arguments are cached when calling 
-:code:`.marginal_likelihood` on :code:`gp`.
+:math:`f`.  This is because those arguments are cached when 
+:code:`.marginal_likelihood` is called on :code:`gp`.
 
 .. note::
   When constructing conditionals, the additional arguments :code:`X`, :code:`y`,