docs(guide/Directives): fix link formatting

Closes #12909;

Author: Narretz

Diff for: docs/content/guide/directive.ngdoc

@@ -43,8 +43,7 @@ mirrors the process of compiling source code in
 Before we can write a directive, we need to know how Angular's {@link guide/compiler HTML compiler}
 determines when to use a given directive.
 
-Similar to the terminology used when an [element **matches** a selector]
-(https://developer.mozilla.org/en-US/docs/Web/API/Element.matches), we say an element **matches** a
+Similar to the terminology used when an [element **matches** a selector](https://developer.mozilla.org/en-US/docs/Web/API/Element.matches), we say an element **matches** a
 directive when the directive is part of its declaration.
 
 In the following example, we say that the `<input>` element **matches** the `ngModel` directive