Upgrade to CodeMirror 5.8
Review Request #7745 — Created Oct. 29, 2015 and submitted — Latest diff uploaded
This patch upgrades CodeMirror 5.8, which is the first released version
to include the new custom style overrides for Markdown (see commit
db3386f). This patch also brings in to line the requirements for using
the landed version of the patch (instead of the original, unreviewed
patch we were using before).
Ran JS tests.