build: move ember-modifer to dependencies (#381)

Author: jkusa

package-lock.json

@@ -43,7 +43,6 @@
     "ember-disable-prototype-extensions": "^1.1.3",
     "ember-fn-helper-polyfill": "^1.0.2",
     "ember-load-initializers": "^2.1.2",
-    "ember-modifier": "^2.1.2",
     "ember-named-arguments-polyfill": "^1.0.0",
     "ember-page-title": "^7.0.0",
     "ember-qunit": "^5.1.5",
@@ -76,6 +75,7 @@
     "ember-auto-import": "^2.4.2",
     "ember-cli-babel": "^7.26.11",
     "ember-cli-htmlbars": "^6.1.0",
+    "ember-modifier": "^3.2.7",
     "prop-types": "^15.8.1"
   },
   "keywords": [