.log doesn't properly escape quotes

[marcoceppi]

Causing the following to occur:

co Ceppi" ],[ "81735deeacf3c050b1f73e8923f785cb6c5f5e2d", "Tweaked "messages""
                                                                    ^
SyntaxError: Unexpected token m
    at Object.parse (native)
    at module.exports.log (/home/marco/Projects/ondina/control-panel/node_modules/git-rev/index.js:25:17)
    at /home/marco/Projects/ondina/control-panel/node_modules/git-rev/index.js:5:5
    at ChildProcess.exithandler (child_process.js:538:7)
    at ChildProcess.EventEmitter.emit (events.js:96:17)
    at maybeClose (child_process.js:638:16)
    at Socket.ChildProcess.spawn.stdin (child_process.js:815:11)
    at Socket.EventEmitter.emit (events.js:93:17)
    at Socket._destroy.destroyed (net.js:357:10)
    at process.startup.processNextTick.process._tickCallback (node.js:244:9)

[marcoceppi]

I've committed a "fix" for this, it's not my favorite so I'm curious your feedback on this. It also introduces a new dependency. Not sure if this is okay. If not there are ways to mock that one async method.