npm install gulp-ngbuild
var gulp = require("gulp");
var ngbuild = require("gulp-ngbuild");
gulp.task("ngbuild", function () {
gulp.src("app/app.js")
.pipe(ngbuild())
.pipe(gulp.dest("app_build"));
});
gulp.task("watch", function () {
gulp.watch(["app/**/*"],["ngbuild"]);
});