Move acorn to dependency

We dont really need it but its needed for Standard and gulp-sourcemaps.

Heroku removes dev dependency by default.

package.json

@@ -12,6 +12,7 @@
     "test": "npm run lint && gulp generate-assets && jest"
   },
   "dependencies": {
+    "acorn": "^6.0.5",
     "ansi-colors": "^3.2.3",
     "basic-auth": "^2.0.0",
     "basic-auth-connect": "^1.0.0",
@@ -51,7 +52,6 @@
     ]
   },
   "devDependencies": {
-    "acorn": "^6.0.5",
     "jest": "^23.6.0",
     "standard": "^12.0.1",
     "supertest": "^3.0.0"