Those are conflict markers, meaning that you messed up your git merge. When a merge isn’t resolved automatically, git leaves the index and the working tree in a special state that gives you all the information you need to help resolve the merge.
So, basically, it means 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.
See Git conflict markers for more information on your problem, and follow this guide to get rid of them.
To follow up with an example taken from Git merge left HEAD marks in my files:
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(""); }