docs(compile): fix minor spelling mistake

Closes: #3468

src/ng/compile.js

@@ -168,7 +168,7 @@ function $CompileProvider($provide) {
    * @function
    *
    * @description
-   * Register a new directives with the compiler.
+   * Register a new directive with the compiler.
    *
    * @param {string} name Name of the directive in camel-case. (ie <code>ngBind</code> which will match as
    *                <code>ng-bind</code>).