Replace `source :rubygems` with https url for rubygems.org

Builder 1.3.2 complained:
The source :rubygems is deprecated because HTTP requests are insecure.
Please change your source to 'https://rubygems.org' if possible, or 'http://rubygems.org' if not.
Merge pull request #415 from fiapps/master

Replace `source :rubygems` with https url for rubygems.org in Gemfile
Some cleanup of dependents
Removing IEEE dependent styles to avoid duplicates when adding IEEE dependent generated automatically with the script in the CSL-utilities repository.
Adding IEEE dependents generated automatically with the script in the csl-utilities repository.
Reverting IEEE dependents which are actually IAP dependents. See https://github.com/citation-style-language/styles/commit/97db7931268f04eafe8b041612c23deb5a05d83f#commitcomment-2796660
Removing styles duplicated by the autogeneration of IOP journals.
Adds IOP dependent styles autogenerated using the script from the csl-utilities repository.
Merge branch 'master' into springer

Conflicts solved:
	dependent/journal-of-optics.csl