Fix clang compilation

Summary: Fix shadowed variable name

Test Plan: compile

Reviewed By: mmandal@fb.com

Subscribers: fugalh, mathieubaudet, folly-diffs@

FB internal diff: D1732033

Signature: t1:1732033:1418250864:d460fea376ac93c05b86977629b95dac60b8b916

folly/experimental/wangle/rx/Observable.h

@@ -94,9 +94,9 @@ class Observable {
     // helper class.
     struct ViaSubject : public Observable<T>
     {
-      ViaSubject(SchedulerPtr scheduler,
+      ViaSubject(SchedulerPtr sched,
                  Observable* obs)
-        : scheduler_(scheduler), observable_(obs)
+        : scheduler_(sched), observable_(obs)
       {}
 
       Subscription<T> subscribe(ObserverPtr<T> o) override {