Problema com o gulpfile.js

Esta dando erro ao rodar o gulp

MBP-de-os:projeto osx$ sudo npm run gulp build-img

> projeto@1.0.0 gulp /Users/osx/Documents/Estudo/Alura/projeto
> gulp "build-img"

/Users/osx/Documents/Estudo/Alura/projeto/gulpfile.js:4
gulp.task('build-img', functio(){
                               ^

SyntaxError: missing ) after argument list
    at exports.runInThisContext (vm.js:53:16)
    at Module._compile (module.js:373:25)
    at Object.Module._extensions..js (module.js:416:10)
    at Module.load (module.js:343:32)
    at Function.Module._load (module.js:300:12)
    at Module.require (module.js:353:17)
    at require (internal/module.js:12:17)
    at Liftoff.handleArguments (/Users/osx/Documents/Estudo/Alura/projeto/node_modules/gulp/bin/gulp.js:116:3)
    at Liftoff.<anonymous> (/Users/osx/Documents/Estudo/Alura/projeto/node_modules/gulp/node_modules/liftoff/index.js:198:16)
    at module.exports (/Users/osx/Documents/Estudo/Alura/projeto/node_modules/gulp/node_modules/liftoff/node_modules/flagged-respawn/index.js:17:3)

npm ERR! Darwin 16.3.0
npm ERR! argv "/usr/local/bin/node" "/usr/local/bin/npm" "run" "gulp" "build-img"
npm ERR! node v4.4.4
npm ERR! npm  v2.15.1
npm ERR! code ELIFECYCLE
npm ERR! projeto@1.0.0 gulp: `gulp "build-img"`
npm ERR! Exit status 1
npm ERR! 
npm ERR! Failed at the projeto@1.0.0 gulp script 'gulp "build-img"'.
npm ERR! This is most likely a problem with the projeto package,
npm ERR! not with npm itself.
npm ERR! Tell the author that this fails on your system:
npm ERR!     gulp "build-img"
npm ERR! You can get information on how to open an issue for this project with:
npm ERR!     npm bugs projeto
npm ERR! Or if that isn't available, you can get their info via:
npm ERR! 
npm ERR!     npm owner ls projeto
npm ERR! There is likely additional logging output above.

npm ERR! Please include the following file with any support request:
npm ERR!     /Users/osx/Documents/Estudo/Alura/projeto/npm-debug.log

O codigo do gulpfile.js esta assim:

var gulp = require('gulp'),
    imagemin = require('gulp-imagemin');

gulp.task('build-img', functio(){

    gulp.src('src/img/**/*') // origem
        .pipe(imagemin())
        .pipe(gulp.dest('src/img'));
});