[Bug #936837] Add missing word

Doc/api/abstract.tex

@@ -573,7 +573,7 @@ determination.
 
 \begin{cfuncdesc}{PyObject*}{PyNumber_InPlaceFloorDivide}{PyObject *o1,
                                                           PyObject *o2}
-  Returns the mathematical of dividing \var{o1} by \var{o2}, or
+  Returns the mathematical floor of dividing \var{o1} by \var{o2}, or
   \NULL{} on failure.  The operation is done \emph{in-place} when
   \var{o1} supports it.  This is the equivalent of the Python
   statement \samp{\var{o1} //= \var{o2}}.