Fix codestyle for typeof comparison (facebook#19928)

Author: ehpc

packages/react-reconciler/src/ReactFiberHooks.new.js

@@ -1248,7 +1248,7 @@ function mountEffect(
 ): void {
   if (__DEV__) {
     // $FlowExpectedError - jest isn't a global, and isn't recognized outside of tests
-    if ('undefined' !== typeof jest) {
+    if (typeof jest !== 'undefined') {
       warnIfNotCurrentlyActingEffectsInDEV(currentlyRenderingFiber);
     }
   }
@@ -1276,7 +1276,7 @@ function updateEffect(
 ): void {
   if (__DEV__) {
     // $FlowExpectedError - jest isn't a global, and isn't recognized outside of tests
-    if ('undefined' !== typeof jest) {
+    if (typeof jest !== 'undefined') {
       warnIfNotCurrentlyActingEffectsInDEV(currentlyRenderingFiber);
     }
   }
@@ -1771,7 +1771,7 @@ function dispatchAction<S, A>(
     }
     if (__DEV__) {
       // $FlowExpectedError - jest isn't a global, and isn't recognized outside of tests
-      if ('undefined' !== typeof jest) {
+      if (typeof jest !== 'undefined') {
         warnIfNotScopedWithMatchingAct(fiber);
         warnIfNotCurrentlyActingUpdatesInDev(fiber);
       }