Typo fix.

Doc/api/exceptions.tex

@@ -129,7 +129,7 @@ for each thread.
 
 \begin{cfuncdesc}{PyObject*}{PyErr_Format}{PyObject *exception,
                                            const char *format, \moreargs}
-  This function sets the error indicator and returns \NULL..
+  This function sets the error indicator and returns \NULL.
   \var{exception} should be a Python exception (string or class, not
   an instance).  \var{format} should be a string, containing format
   codes, similar to \cfunction{printf()}. The \code{width.precision}