How to avoid 'git push' error after 'site-deploy'?

[Dan Rollo]

I'm enjoying the maven-gitsite plugin.

I may be doing something wrong, but I continue to run into a problem
where, after I successfully do a 'mvn site-deploy' to git hub, the
next time I attempt to do 'git push', I get an error like the one
below:

$ git push
To g...@github.com:bhamail/maven-artifactory-plugin.git
! [rejected] gh-pages -> gh-pages (non-fast-forward)
error: failed to push some refs to 'g...@github.com:bhamail/maven-
artifactory-plugin.git'
To prevent you from losing history, non-fast-forward updates were
rejected
Merge the remote changes before pushing again. See the 'Note about
fast-forwards' section of 'git push --help' for details.

I've tried doing 'git pull' after completing 'mvn site-deploy', but
that does not seem to help.
I'm working on my 'master' branch:

$ git branch
gh-pages
* master

Any suggestions?

Thanks,
Dan