Replace var to const in Libraries/Utilities/deepFreezeAndThrowOnMutationInDev-test.js (#22110)

Summary:
Replaces the keywords var to const in Libraries/Utilities/deepFreezeAndThrowOnMutationInDev.js

- [x]  Check npm run flow
- [x]  Check npm run flow-check-ios
- [x]  Check npm run flow-check-android

[GENERAL] [ENHANCEMENT] [Libraries/Utilities/deepFreezeAndThrowOnMutationInDev.js] - replace var
Pull Request resolved: #22110

Differential Revision: D12919284

Pulled By: TheSavior

fbshipit-source-id: 4a3a3f4c49665c538ed5f38f3cc2142d40ac4d55

Author: watanabeyu

Libraries/Utilities/__tests__/deepFreezeAndThrowOnMutationInDev-test.js

@@ -28,7 +28,7 @@ describe('deepFreezeAndThrowOnMutationInDev', function() {
 
   it('should not throw on object without prototype', () => {
     __DEV__ = true;
-    var o = Object.create(null);
+    const o = Object.create(null);
     o.key = 'Value';
     expect(() => deepFreezeAndThrowOnMutationInDev(o)).not.toThrow();
   });
@@ -134,7 +134,7 @@ describe('deepFreezeAndThrowOnMutationInDev', function() {
     expect(o.key1.key2).toBe('newValue');
   });
 
-  it("shouldn't recurse infinitely", () => {
+  it('shouldn\'t recurse infinitely', () => {
     __DEV__ = true;
     const o = {};
     o.circular = o;