Bump ember-cli from 3.18.0 to 3.20.0

Bumps [ember-cli](https://github.com/ember-cli/ember-cli) from 3.18.0 to 3.20.0.
- [Release notes](https://github.com/ember-cli/ember-cli/releases)
- [Changelog](https://github.com/ember-cli/ember-cli/blob/master/CHANGELOG.md)
- [Commits](ember-cli/ember-cli@v3.18.0...v3.20.0)

Signed-off-by: dependabot-preview[bot] <[email protected]>

Author: dependabot-preview[bot]

package.json

@@ -64,7 +64,7 @@
     "co": "^4.6.0",
     "console-ui": "^3.1.1",
     "core-object": "^3.1.5",
-    "ember-cli": "~3.18.0",
+    "ember-cli": "~3.20.0",
     "ember-cli-app-version": "^3.2.0",
     "ember-cli-babel": "^7.22.1",
     "ember-cli-dependency-checker": "^3.2.0",