Grunt: extend `prep-release` task.

Make it so that everything is done for us to reduce the possibility of missing something when releasing.

Gruntfile.js

@@ -515,7 +515,7 @@ module.exports = function (grunt) {
   grunt.registerTask('lint-docs-js', ['jshint:assets', 'jscs:assets']);
   grunt.registerTask('docs', ['docs-css', 'lint-docs-css', 'docs-js', 'lint-docs-js', 'clean:docs', 'copy:docs', 'build-glyphicons-data', 'build-customizer']);
 
-  grunt.registerTask('prep-release', ['jekyll:github', 'htmlmin', 'compress']);
+  grunt.registerTask('prep-release', ['dist', 'docs', 'jekyll:github', 'htmlmin', 'compress']);
 
   // Task for updating the cached npm packages used by the Travis build (which are controlled by test-infra/npm-shrinkwrap.json).
   // This task should be run and the updated file should be committed whenever Bootstrap's dependencies change.