[core] Fix performance-unnecessary-value-param errors in header files

As reported by clang-tidy-8.

1 files changed, 1 insertions, 1 deletions

diff --git a/include/mbgl/actor/scheduler.hpp b/include/mbgl/actor/scheduler.hpp
index cdaf185c8b..1a9ba1907f 100644
--- a/include/mbgl/actor/scheduler.hpp
+++ b/include/mbgl/actor/scheduler.hpp
@@ -90,7 +90,7 @@ protected:
     template <typename TaskFn, typename ReplyFn>
     void scheduleAndReplyValue(const TaskFn& task,
                                const ReplyFn& reply,
-                               mapbox::base::WeakPtr<Scheduler> replyScheduler) {
+                               const mapbox::base::WeakPtr<Scheduler>& replyScheduler) {
         auto scheduled = [replyScheduler, task, reply] {
             auto lock = replyScheduler.lock();
             if (!replyScheduler) return;