docs(guide.unit-testing): fix typo

Author: TimothyAhong

docs/content/guide/dev_guide.unit-testing.ngdoc

@@ -3,7 +3,7 @@
 @description
 
 JavaScript is a dynamically typed language which comes with great power of expression, but it also
-come with almost no-help from the compiler. For this reason we feel very strongly that any code
+comes with almost no-help from the compiler. For this reason we feel very strongly that any code
 written in JavaScript needs to come with a strong set of tests. We have built many features into
 Angular which makes testing your Angular applications easy. So there is no excuse for not testing.