Fix the Cancel button text in Add Plugin Repository window

Fix the Cancel button text to show "Cancel" instead of "Can...".

Steps to reproduce:

1. Start IGB
2. Go to Preferences and select App Repositories tab
3. Click Add... Button
4. A new window pops up to add a new plugin repository.
5. In this window, the Cancel button text is shown as "Can..." instead of "Cancel". (even if you resize the window the text looks same)

Note: I think it should work if you change the size of the Cancel button to fit the text