Using deprecated $http callback methods.

[Angus Whitehead]

The $http custom callback methods success() and error() have been removed from angular 1.6. angular/angular.js@b54a39e

Currently I get the following error using angular-notify:

TypeError: $http.get(...).success is not a function
    at notify (webpack:///./~/angular-notify/dist/angular-notify.js?:39)

The standard then() and catch() methods are compatible with older versions so should be used instead.

This should be a minor change, I will submit a PR.

[Angus Whitehead]

Closed as fixed by 4e6ea95.