removed unnecessary git checkout for bug, feature and refactor

In ubuntu, when I run git bug|feature|refactor I get this error:
```
error: pathspec 'bug/test' did not match any file(s) known to git.
fatal: Unable to create '/var/www/leanin/.git/index.lock': File exists.

If no other git process is currently running, this probably means a
git process crashed in this repository earlier. Make sure no other git
process is running and remove the file manually to continue.
```

`git checkout -b [branch]` automatically puts you in that branch, so I removed that line and it works in ubuntu now.