Update dependency ember-source to ~3.20.0

Author: renovate-bot

package.json

@@ -44,7 +44,7 @@
     "ember-maybe-import-regenerator": "^0.1.6",
     "ember-qunit": "^4.5.1",
     "ember-resolver": "^7.0.0",
-    "ember-source": "~3.16.0",
+    "ember-source": "~3.20.0",
     "ember-source-channel-url": "^2.0.1",
     "ember-try": "^1.2.1",
     "eslint-config-sane": "^0.8.5",