MEAN堆栈：未定义角度

I have been searching for answer to my problem for two full days now without results. I know there are a lot of threads about "angular is not defined", but their answers have been of no avail. The starting point is that I have deployed MEAN stack for a SPA on DigitalOcean. There is also grunt in use. The app has been running successfully right until grunt tries to run the server.js file which has angular.module(... call. I have been searching for answer to my problem