Those are conflict markers. You’re still in the process of merging, but there were some parts that Git couldn’t merge automatically. You’ll need to hand-edit those parts to what you want them to be and then commit the results.
For instance, in your particular case, you’d probably want to resolve it like this (note – the arrows/text on the right are just my notes, not something you’d type into the file):
integer =
<<<<<<< HEAD <-+ remove the bits here
digits:[0-9]+ |
{ return digits.join(""); } |
======= <-+
sign:"-"* digits:[0-9]+
{ return sign + digits.join(""); }
>>>>>>> gh-pages <-- and this
and thus you’d save the file as…
integer =
sign:"-"* digits:[0-9]+
{ return sign + digits.join(""); }