Fix new clippy lints

src/librustdoc/passes/calculate_doc_coverage.rs

@@ -118,7 +118,7 @@ fn limit_filename_len(filename: String) -> String {
     }
 }
 
-impl<'a, 'b> CoverageCalculator<'a, 'b> {
+impl CoverageCalculator<'_, '_> {
     fn to_json(&self) -> String {
         serde_json::to_string(
             &self
@@ -188,7 +188,7 @@ impl<'a, 'b> CoverageCalculator<'a, 'b> {
     }
 }
 
-impl<'a, 'b> DocVisitor<'_> for CoverageCalculator<'a, 'b> {
+impl DocVisitor<'_> for CoverageCalculator<'_, '_> {
     fn visit_item(&mut self, i: &clean::Item) {
         if !i.item_id.is_local() {
             // non-local items are skipped because they can be out of the users control,