Replace 'use babel' -> '@babel' in comment directive

build/lib/uses-babel.coffee

@@ -3,7 +3,7 @@ fs = require 'fs'
 BABEL_PREFIXES = [
   "'use babel'"
   '"use babel"'
-  '/** use babel */'
+  '/** @babel */'
 ]
 
 PREFIX_LENGTH = Math.max(BABEL_PREFIXES.map((prefix) -> prefix.length)...)

spec/babel-spec.coffee

@@ -1,5 +1,5 @@
 describe "Babel transpiler support", ->
-  describe 'when a .js file starts with /** use babel */;', ->
+  describe 'when a .js file starts with /** @babel */;', ->
     it "transpiles it using babel", ->
       transpiled = require('./fixtures/babel/babel-comment.js')
       expect(transpiled(3)).toBe 4

spec/fixtures/babel/babel-comment.js

@@ -1,3 +1,3 @@
-/** use babel */
+/** @babel */
 
 module.exports = v => v + 1

src/babel.js

@@ -10,7 +10,7 @@ let babelVersionDirectory = null
 const defaultOptions = require('../static/babelrc.json')
 
 exports.shouldCompile = function(sourceCode) {
-  return sourceCode.startsWith('/** use babel */') ||
+  return sourceCode.startsWith('/** @babel */') ||
     sourceCode.startsWith('"use babel"') ||
     sourceCode.startsWith("'use babel'")
 }