You should:

1. Update any scripts you have to be aware of 5.0.x as a branch

2. Synchronize your fork using sync_with_upstream from https://github.com/maniksurtani/githelpers (make sure you update the script as per step 1)

3. Rebase any of your topic branches.  Stash any unsaved work, $ git rebase master if your topic branch is for 5.1.  You don't need to rebase if your topic branch was for 5.0.

4.  Un-stash your work.

Check all of your branches using 

$ git log --pretty=oneline --graph --abbrev-commit --decorate 

to make sure they are what you expect.  :)

Cheers

Manik