remove coveralls from gruntfile (close vuejs#960)

Author: yyx990803

gruntfile.js

@@ -75,7 +75,6 @@ module.exports = function (grunt) {
   // load npm tasks
   grunt.loadNpmTasks('grunt-contrib-jshint')
   grunt.loadNpmTasks('grunt-karma')
-  grunt.loadNpmTasks('grunt-coveralls')
 
   // load custom tasks
   require('./build/grunt-tasks/build')(grunt)
@@ -91,6 +90,4 @@ module.exports = function (grunt) {
   grunt.registerTask('ci', ['jshint', 'cover', 'codecov', 'build', 'casper', 'sauce'])
   grunt.registerTask('default', ['jshint', 'build', 'test'])
 
-  grunt.registerTask('debug', ['coveralls', 'build'])
-
 }