cluster: fix permanent deoptimizations

PR-URL: https://github.com/nodejs/node/pull/12456
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/internal/cluster/child.js

@@ -99,7 +99,7 @@ function shared(message, handle, indexesKey, cb) {
     delete handles[key];
     delete indexes[indexesKey];
     return close.apply(this, arguments);
-  };
+  }.bind(handle);
   assert(handles[key] === undefined);
   handles[key] = handle;
   cb(message.errno, handle);
@@ -192,7 +192,7 @@ function _disconnect(masterInitiated) {
     }
   }
 
-  for (const key in handles) {
+  for (var key in handles) {
     const handle = handles[key];
     delete handles[key];
     waitingCount++;