Include dotfiles when copying the site

Part one of fixing issue #141.

generators/jekyll/templates/build.js

@@ -7,7 +7,7 @@ const argv = require('yargs').argv;
 // 'gulp jekyll:tmp' -- copies your Jekyll site to a temporary directory
 // to be processed
 gulp.task('site:tmp', () =>
-  gulp.src(['src/**/*', '!src/assets/**/*', '!src/assets'])
+  gulp.src(['src/**/*', '!src/assets/**/*', '!src/assets'], {dot: true})
     .pipe(gulp.dest('.tmp/src'))
     .pipe(size({title: 'Jekyll'}))
 );