ALERT: Merge of #776 caused a bug in kinto.py

[RedBearAK]

@rbreaves

The recent merge of the PR that replaces the rest of the instances of "M" with "Alt" accidentally caught a line that was using the letter "M" as part of the shortcut. So now a fresh install of Kinto is barfing on the line because it's just modifiers.

Faulty line:

    K("RC-Alt"): K("C-Shift-Alt"),

Should be changed back to:

    K("RC-M"): K("C-Shift-M"),

[rbreaves]

Thanks