[DOC] repository_rules: Minor grammar fix
Context: Was perusing after looking here:
Closes
@@ -79,7 +79,7 @@ in the dependency graph (including the WORKSPACE file itself) will
cause an execution of the implementation function.
The implementation function can be _restarted_ if a dependency it
-request is _missing_. The beginning of the implementation function
+requests is _missing_. The beginning of the implementation function
will be re-executed after the dependency has been resolved. To avoid
unnecessary restarts (which are expensive, as network access might
have to be repeated), label arguments are prefetched, provided all
