lib: move deprecationWarned var

The variable deprecationWarned currently looks a little misplaced. It is
used in emitWarning but declared after it. This commit suggest moving
the var to the beginning of the function.

PR-URL: https://github.com/nodejs/node/pull/14769
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Alexey Orlenko <eaglexrlnk@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/internal/process/promises.js

@@ -14,6 +14,8 @@ function getAsynchronousRejectionWarningObject(uid) {
 }
 
 function setupPromises(scheduleMicrotasks) {
+  let deprecationWarned = false;
+
   process._setupPromises(function(event, promise, reason) {
     if (event === promiseRejectEvent.unhandled)
       unhandledRejection(promise, reason);
@@ -73,7 +75,7 @@ function setupPromises(scheduleMicrotasks) {
         'DeprecationWarning', 'DEP0018');
     }
   }
-  var deprecationWarned = false;
+
   function emitPendingUnhandledRejections() {
     let hadListeners = false;
     while (pendingUnhandledRejections.length > 0) {