fix gulpfile to signal completion, clean up a bit

Gulpfile.js

-var gulp = require('gulp');
-var sass = require('gulp-sass');
-var concat = require('gulp-concat');
+const gulp = require('gulp')
+const sass = require('gulp-sass')
+const concat = require('gulp-concat')
 
-gulp.task('styles', function() {
+gulp.task('styles', function(done) {
   gulp.src('styles/**/*.scss')
     .pipe(sass({
         errLogToConsole: true
     }))
     .pipe(gulp.dest('./public/stylesheets/'))
-    .pipe(concat('style.css'));
-});
-
+    .pipe(concat('style.css'))
+  done()
+})