Update CodeMirror dependency#5198

Merged

blink1073 merged 3 commits intojupyter:masterfrom

bzinberg:zeros-crash

May 15, 2020

Commits on Jan 30, 2020

Commits on Jan 31, 2020

Fix place where we were passing an `Array[string]` to `CodeMirror.findModeByExtension` instead of passing a string. (I guess older versions of CodeMirror allowed this?)
bzinberg
committed