docs(router): fix typos

modules/@angular/router/src/directives/router_link.ts

@@ -34,7 +34,7 @@ import {UrlTree} from '../url_tree';
  *
  * @description
  *
- * The RouterLink directives lets you link to specific parts of your app.
+ * The RouterLink directives let you link to specific parts of your app.
  *
  * Whe the link is static, you can use the directive as follows:
  *

modules/@angular/router/src/directives/router_link_active.ts

@@ -16,7 +16,7 @@ import {RouterLink, RouterLinkWithHref} from './router_link';
 
 
 /**
- * @whatItDoes Lets you add a CSS class to an element when the link's route.
+ * @whatItDoes Lets you add a CSS class to an element when the link's route becomes active.
  *
  * @howToUse
  *

modules/@angular/router/src/router_module.ts

@@ -29,7 +29,7 @@ import {flatten} from './utils/collection';
 const ROUTER_DIRECTIVES = [RouterOutlet, RouterLink, RouterLinkWithHref, RouterLinkActive];
 
 /**
- * @whatItDoes Is used in DI to configure router.
+ * @whatItDoes Is used in DI to configure the router.
  * @stable
  */
 export const ROUTER_CONFIGURATION = new OpaqueToken('ROUTER_CONFIGURATION');

modules/@angular/router/src/url_tree.ts

@@ -278,7 +278,7 @@ export abstract class UrlSerializer {
  * /inbox/33;open=true/messages/44
  * ```
  *
- * DefaultUrlSerializer uses parenthesis to serialize secondary segments (e.g., popup:compose), the
+ * DefaultUrlSerializer uses parentheses to serialize secondary segments (e.g., popup:compose), the
  * colon syntax to specify the outlet, and the ';parameter=value' syntax (e.g., open=true) to
  * specify route specific parameters.
  *

modules/@angular/router/testing/router_testing_module.ts

@@ -92,7 +92,8 @@ export function setupTestingRouter(
  * @description
  *
  * The modules sets up the router to be used for testing.
- * It provides spy implementations of Location, LocationStrategy, and NgModuleFactoryLoader.
+ * It provides spy implementations of {@link Location}, {@link LocationStrategy}, and {@link
+ * NgModuleFactoryLoader}.
  *
  * @stable
  */