docs: fix some typos in comments and strings

Couple of typos fixed:
- occuring -> occurring
- imlement -> implement
- idenitifer -> identifer
etc...

Closes #5943

modules/angular2/src/core/di/provider.ts

@@ -161,7 +161,7 @@ export class Provider {
    * expect(injector.get(String)).toEqual('Value: 3');
    * ```
    *
-   * Used in conjuction with dependencies.
+   * Used in conjunction with dependencies.
    */
   useFactory: Function;
 
@@ -211,7 +211,7 @@ export class Provider {
    * Creates multiple providers matching the same token (a multi-provider).
    *
    * Multi-providers are used for creating pluggable service, where the system comes
-   * with some default providers, and the user can register additonal providers.
+   * with some default providers, and the user can register additional providers.
    * The combination of the default providers and the additional providers will be
    * used to drive the behavior of the system.
    *

modules/angular2/src/core/zone/ng_zone.ts

@@ -276,7 +276,7 @@ export class NgZone {
   get hasPendingTimers(): boolean { return this._pendingTimeouts.length > 0; }
 
   /**
-   * Whether there are any outstanding asychnronous tasks of any kind that are
+   * Whether there are any outstanding asynchronous tasks of any kind that are
    * scheduled to run within Angular zone.
    *
    * Useful as a signal of UI stability. For example, when a test reaches a