Fix Windows spawn issues, switch to cross-spawn

Fixes #397. sqlformat should not be able to be found and used.

See https://github.com/joyent/node/issues/2318

package.json

@@ -59,6 +59,7 @@
     "bluebird": "^2.9.27",
     "coffee-fmt": "0.11.0",
     "coffee-formatter": "^0.1.2",
+    "cross-spawn": "^0.4.1",
     "csscomb": "^3.1.7",
     "diff": "^1.4.0",
     "editorconfig": "^0.12.2",

src/beautifiers/beautifier.coffee

@@ -2,8 +2,7 @@ Promise = require("bluebird")
 _ = require('lodash')
 fs = require("fs")
 temp = require("temp").track()
-exec = require("child_process").exec
-spawn = require("child_process").spawn
+spawn = require('cross-spawn')
 readFile = Promise.promisify(fs.readFile)
 which = require('which')