refactor: Incorrect spelling in hooks error message (#8585)

Author: cbaker6

spec/ParseHooks.spec.js

@@ -208,7 +208,7 @@ describe('Hooks', () => {
           expect(err).not.toBe(null);
           if (err) {
             expect(err.code).toBe(143);
-            expect(err.message).toBe('function name: my_new_function already exits');
+            expect(err.message).toBe('function name: my_new_function already exists');
           }
           return Parse.Hooks.removeFunction('my_new_function');
         }

src/Controllers/HooksController.js

@@ -144,7 +144,7 @@ export class HooksController {
     if (aHook.functionName) {
       return this.getFunction(aHook.functionName).then(result => {
         if (result) {
-          throw new Parse.Error(143, `function name: ${aHook.functionName} already exits`);
+          throw new Parse.Error(143, `function name: ${aHook.functionName} already exists`);
         } else {
           return this.createOrUpdateHook(aHook);
         }