Update to Pym v1.2.0

[benlk]

Changes

• Update to pym.js version 1.2.0: https://github.com/nprapps/pym.js/releases/tag/v1.2.0 (Changelog at https://github.com/nprapps/pym.js/blob/v1.2.0/CHANGELOG )
• Bump plugin version number to 1.2.0

Since the 1.1.2 -> 1.2.0 release does not break compatibility with existing versions of Pym, we don't have to deal with providing an old version of pym to old shortcodes and new versions of pym to new shortcodes. I've created an issue for discussion on that: #15