build: Update various devDependencies to latest

grunt-css-url-embed: 1.0.3 -> 1.0.4 (1.1.0 and above will need local changes)
grunt-jscs: 0.7.1 -> 0.8.1
karma: 0.12.24 -> 0.12.25

No-op; note that the grunt-jscs change switches us from jscs 1.6.0 to
1.7.2, which provides some new options (unused in the Wikimedia preset).

Change-Id: Iffde19b7b55969c480b4d64826f4aecbe346746f