Fix copy-paste error in docs.

doc/library/config.txt

@@ -465,8 +465,8 @@ import theano and print the config variable, as in:
 
     .. note::
 
-        This could cause memory fragmentation. So if you have a
-        memory error while using CNMeM, try to allocate more memory at
+        This could cause memory fragmentation. So if you have a memory
+        error while using the cache, try to allocate more memory at
         the start or disable it. If you try this, report your result
         on :ref`theano-dev`.