update codemirror

[Almenon]

new codemirror contains several new features and bug fixes of note:

• python mode: Highlight expressions inside format strings.
• python mode: Improve tokenizing of operators.
• match-highlighter addon: Fix problem with matching words that have regexp special syntax in them.
• sublime bindings: Fix addCursorToSelection for short lines.
• sublime bindings: Fix the toggleBookmark command.
• sublime bindings: Use the proper key bindings for addCursorToNextLine and addCursorToPrevLine.
• sublime bindings: Add extend-selection (Ctrl-Alt- or Cmd-Shift-Up/Down).
• search addon: Fix crash when restarting search after doing empty search.

Maybe I can install codemirror as a npm package this time - I forget why I couldn't do that before, I ran into some issue.

[Almenon]

while I'm at it may as well update electron too. And anything else that needs updating. renderJSON, for example.