skip imagemin gulp task during CI to save a couple of minutes

gulpfile.js

@@ -57,6 +57,9 @@ function optimizeHtml() {
 }
 
 function optimizeImages() {
+  // allow skipping this step via an env variable to save time during CI, etc.
+  if (process.env.SKIP_OPTIMIZE_IMAGES === "true") return Promise.resolve("skipped");
+
   return gulp
     .src(["public/**/*.{gif,jpg,jpeg,png,svg}", "!public/assets/emoji/**/*"], { base: "./" })
     .pipe(