Add a missing space.

Doc/ref/ref3.tex

@@ -1185,7 +1185,7 @@ keys.
 \end{methoddesc}
 
 \begin{methoddesc}[object]{__hash__}{self}
-Called for the key object for dictionary\obindex{dictionary}
+Called for the key object for dictionary \obindex{dictionary}
 operations, and by the built-in function
 \function{hash()}\bifuncindex{hash}.  Should return a 32-bit integer
 usable as a hash value