docs(*): fix spelling errors

Closes #16942

CONTRIBUTING.md

@@ -172,7 +172,7 @@ restarted.
     git push origin my-fix-branch -f
     ```
 
-    This is generally easier to follow, but seperate commits are useful if the Pull Request contains
+    This is generally easier to follow, but separate commits are useful if the Pull Request contains
     iterations that might be interesting to see side-by-side.
 
 That's it! Thank you for your contribution!

src/ng/compile.js

@@ -1026,7 +1026,7 @@
  *
  * When the original node and the replace template declare the same directive(s), they will be
  * {@link guide/compiler#double-compilation-and-how-to-avoid-it compiled twice} because the compiler
- * does not deduplicate them. In many cases, this is not noticable, but e.g. {@link ngModel} will
+ * does not deduplicate them. In many cases, this is not noticeable, but e.g. {@link ngModel} will
  * attach `$formatters` and `$parsers` twice.
  *
  * See issue [#2573](https://github.com/angular/angular.js/issues/2573).

test/ng/directive/selectSpec.js

@@ -349,7 +349,7 @@ describe('select', function() {
     });
 
 
-    it('should only call selectCtrl.writeValue after a digest has occured', function() {
+    it('should only call selectCtrl.writeValue after a digest has occurred', function() {
       scope.mySelect = 'B';
       scope.$apply();