1.4.1

• added the new checkToken function
• when a subscription receives a jwtTokenExpired notification, an event jwtTokenExpired is fired
• added a timer to events: the same event can't be fired multiple times if it has been fired before the timeout is reached
• empties the jwtToken property when encountering a jwtTokenExpired error or notification
• updated the travis build so that the dist folder is only generated when building the master branch