Update tasks/istatic.js

支持grunt0.4
Update tasks/istatic.js

让其他任务能依赖istatic（比如`grunt.registerTask('default', ['istatic','jshint'])`）
Merge pull request #1 from dexteryy/patch-1

Update tasks/istatic.js
Merge pull request #1 from mockee/master

Support Grunt 4.0