Bugfix - Typos

Summary:
Fixed few typos in `./Examples` and `./Libraries` folders.
Closes https://github.com/facebook/react-native/pull/4788

Reviewed By: svcscm

Differential Revision: D2759918

Pulled By: androidtrunkagent

fb-gh-sync-id: d692b5c7f561822353e522f9d4dfde7e60b491cf

Examples/UIExplorer/UIExplorerUnitTests/LayoutSubviewsOrderingTest.m

@@ -14,7 +14,7 @@
 /**
  * This test exists to insure that didLayoutSubviews is always called immediately after layoutSubviews for a VC:View
  * pair. In Catalyst we have multiple levels of ViewController containment, and we rely on this ordering
- * to insure that layoutGuides are set on RKViewControllers before Views further down in the heirarchy have
+ * to insure that layoutGuides are set on RKViewControllers before Views further down in the hierarchy have
  * their layoutSubviews called (and need to use the aforementioned layoutGuides)
  */
 - (void)testLayoutSubviewsOrdering
@@ -63,7 +63,7 @@
     }
   }] viewDidLayoutSubviews];
 
-  // setup View heirarchy and force layout
+  // setup View hierarchy and force layout
   parentVC.view = parentView;
   childVC.view = childView;
   [parentVC addChildViewController:childVC];

Examples/UIExplorer/UIExplorerUnitTests/RCTContextExecutorTests.m

@@ -98,7 +98,7 @@ static uint64_t _get_time_nanoseconds(void)
 {
 /**
  * Since we almost don't change the RCTContextExecutor logic, and this test is
- * very likely to become flaky (specially accross different devices) leave it
+ * very likely to become flaky (specially across different devices) leave it
  * to be run manually
  *
  * Previous Values: If you change the executor code, you should update this values