Fix `recently-pushed-branches-enhancements` positioning in responsive views #2940

1. Push new branch to your repo

2. Visit the Issues page, e.g. https://github.com/sindresorhus/refined-github/issues

   <img width="1054" alt="regular" src="https://user-images.githubusercontent.com/1402241/77656223-d85b3680-6f73-11ea-80af-2640be061d71.png">

3. Resize window to ~500px

4. Notice wrong position of widget

   <img width="500" alt="wrong" src="https://user-images.githubusercontent.com/1402241/77656233-dd1fea80-6f73-11ea-98a9-eeea55da4192.png">

I'd expect:

• appear next to the notifications bell
• appear as a small square that expands on hover, maybe just the green button