Update RocketChat plugin to v1.0.7

[oliviermaridat]

Dear @fguillot

I am willing to maintain the RocketChat plugin. My company is using it and therefore me or my colleagues will be able to update it.

If you are ok with, could you consider to accept this MR:

• RocketChat plugin now targets https://github.com/oliviermaridat/plugin-rocketchat instead of the not maintained https://github.com/kanboard/plugin-rocketchat
• Update RocketChat plugin to v1.0.7 : see release note