Merge pull request #89 from floatdrop/master

Exit with code 1 when got errored tasks
3.2.3
More helpful suggestion on how to npm install gulp

Useful for when user only did npm install gulp -g
Merge pull request #94 from floatdrop/master

Wrong placement of error handling function
Merge pull request #93 from Dashed/patch-1

More helpful suggestion on how to npm install gulp
3.2.4
Right implementation of Gulp.prototype.run