Fix private information disclosure

[alexcoman]

Travis-CI will log every command and in order to avoid information disclosure the command should not contain plain text data.

With this patch the log will look like:

** Execute site:deploy
git config --global user.name '$GIT_NAME'
git config --global user.email '$GIT_EMAIL'
git config --global push.default simple
git clone https://$GIT_NAME:$GH_TOKEN@github.com/[...]

and without it:

** Execute site:deploy
git config --global user.name 'm....r'
git config --global user.email '....@martinfenner.org'
git config --global push.default simple
git clone https://m.....r:14.....................f8@github.com/openingscience/openingscience.github.io.git ../openingscience.github.io/

Thanks,
Alex