Merge branch 'bugfix/github_deploy' into 'master'

fix deploy to GitHub

Previous change to gitlab-ci.yml moved setting of Gitlab ssh key to global before_script.
This together with the fact that we used `echo >>` instead of `echo >` to write to `id_rsa_base64` file caused wrong key to be used while pushing to GitHub.
Therefore:
- don't run default before_script before push_master_to_github job
- replace echo >> with echo > to avoid mistakes in the future

See merge request !82

diff --cc .gitlab-ci.yml
Simple merge