remove trailing space

Co-authored-by: NRémy Rakic <remy.rakic+github@gmail.com>

compiler/rustc_typeck/src/check/region.rs

@@ -801,7 +801,7 @@ fn visit_local(&mut self, l: &'tcx Local<'tcx>) {
 /// Performance: This is a query rather than a simple function to enable
 /// re-use in incremental scenarios. We may sometimes need to rerun the
 /// type checker even when the HIR hasn't changed, and in those cases
-/// we can avoid reconstructing the region scope tree. 
+/// we can avoid reconstructing the region scope tree.
 pub fn region_scope_tree(tcx: TyCtxt<'_>, def_id: DefId) -> &ScopeTree {
     let typeck_root_def_id = tcx.typeck_root_def_id(def_id);
     if typeck_root_def_id != def_id {