title: gulp-tag-version running command?
body: <p>I installed gulp-tag-version, but when I am running the command 'gulp tag v1.1.1', it will not confirm this as a task</p>
  
  <pre><code>var gulp = require('gulp');
  var tag_version = require('gulp-tag-version');  
  
  gulp.task('tag', function() {
    return gulp.src(['./package.json']).pipe(tag_version());
  });
  </code></pre>
  
  <p>So what am I doing wrong ?</p>