Improve check update feature

[LordRibblesdale]

In src/Update/UpdateRepo class, the constructor checks if there are updates basing on last release of the project.
I used GitHub APIs by Kohsuke and they needed personal access token to access GitHub database.
I made a read only repository token but I don't feel confortable to implement a pka, even if it is a read only one to get APIs working. (PS: I had to separate key in two strings to let GitHub push changes)
Thanks in advance for alternatives!