Updated docs for $firebaseAuth.$signOut()

Author: jwngr

docs/migration/1XX-to-2XX.md

@@ -52,7 +52,7 @@ Several authentication methods have been renamed and / or have different method
 | `$changeEmail(credentials)` | `$updateEmail(newEmail)` | Changes the email of the currently signed-in user |
 | `$changePassword(credentials)` | `$updatePassword(newPassword)` | Changes the password of the currently signed-in user |
 | `$resetPassword(credentials)` | `$sendPasswordResetEmail(email)` | |
-| `$unauth()` | `$signOut()` | |
+| `$unauth()` | `$signOut()` | Now returns a `Promise`|
 | `$onAuth(callback)` | `$onAuthStateChanged(callback)` | |
 | `$requireAuth()` | `$requireSignIn()` | |
 | `$waitForAuth()` | `$waitForSignIn()` | |

docs/reference.md

@@ -752,8 +752,8 @@ offAuth();
 
 ### $signOut()
 
-Unauthenticates a client from the Firebase Database. It takes no arguments and returns no value.
-When called, the `$onAuthStateChanged()` callback(s) will be triggered.
+Signs out a client. It takes no arguments and returns a `Promise` when the client has been signed
+out. Upon fulfillment, the `$onAuthStateChanged()` callback(s) will be triggered.
 
 ```html
 <span ng-show="firebaseUser">