Update dependency ember-concurrency to v4

Author: renovate[bot]

ember/package.json

@@ -63,7 +63,7 @@
     "ember-cli-sass": "10.0.1",
     "ember-cli-uglify": "3.0.0",
     "ember-click-outside": "2.0.0",
-    "ember-concurrency": "1.3.0",
+    "ember-concurrency": "4.0.4",
     "ember-cookies": "0.5.2",
     "ember-cp-validations": "3.5.6",
     "ember-css-modules": "1.3.4",