How can I uglify a code made in angular.js?

I am trying to minify my code with my code in gulp I can create a folder called _build where I optimize my code, minifying it and returning it uglify and apparently it is minified but it is no longer a valid code for angular.js an example is:

angularRoutingApp.controller('homeController', function($scope,$state,$http,$timeout,$window,alerta,preload){

to

angularRoutingApp.controller("homeController",function(e,o,i,a,n,r,t)

in this line of code is where I convert my controller to uglify

controllers:[$.uglify()],

this is my code:

    gulp.task('minify-js', function() {
      gulp.src('js/*.js')
        .pipe($.uglify())
        .pipe(gulp.dest('./_build/'));
    });

    gulp.task('minify-css', function() {
      gulp.src(['./css/**/*.css'])
        .pipe($.rename({suffix: '.min'}))
        .pipe($.minifyCss({keepBreaks:true}))
        .pipe(gulp.dest('./css/'))
        .pipe(gulp.dest('./_build/css/'));
    });

    gulp.task('minify-html', function() {
      var opts = {
        comments: true,
        spare: true,
        conditionals: true
      };

      gulp.src('./*.html')
        .pipe($.minifyHtml(opts))
        .pipe(gulp.dest('./_build/'));
    });

    gulp.task('fonts', function() {
      gulp.src('./fonts/**/*.{ttf,woff,eof,eot,svg}')
        .pipe($.changed('./_build/fonts'))
        .pipe(gulp.dest('./_build/fonts'));
    });

    gulp.task('server', function(done) {
      return browserSync({
        server: {
          baseDir: './'
        }
      }, done);
    });

    gulp.task('server-build', function(done) {
      return browserSync({
        server: {
          baseDir: './_build/'
        }
      }, done);
    });

    gulp.task('clean:build', function (cb) {
      del([
        './_build/'
        // if we don't want to clean any file we can use negate pattern
        //'!dist/mobile/deploy.json'
      ], cb);
    });

    require('events').EventEmitter.prototype._maxListeners = 100;


    gulp.task('usemin', function() {
      return gulp.src('./index.html')
        // add templates path
        .pipe($.htmlReplace({
          'templates': '<script type="text/javascript" src="js/templates.js"></script>'
        }))
        .pipe($.usemin({
          css: [$.minifyCss(), 'concat'],
          libs: [$.uglify()],
          nonangularlibs: [$.uglify()],
          angularlibs: [$.uglify()],
          controllers:[$.uglify()],
          contservicesapp:[$.uglify()],
          services:[$.uglify()],
          appcomponents: [$.uglify()],
          mainapp: [$.uglify()],
          templates:[$.uglify()],
          directives:[$.uglify()]
        }))
        .pipe(gulp.dest('./_build/'));
    });

how can I solve that?