Correct yarn version (use 3.0.0-beta series).

package.json

@@ -55,7 +55,7 @@
     "ember-maybe-import-regenerator-for-testing": "^1.0.0",
     "ember-native-dom-event-dispatcher": "^0.6.3",
     "ember-resolver": "^4.0.0",
-    "ember-source": "https://s3.amazonaws.com/builds.emberjs.com/canary/shas/5f27c1be4786ae5fde1acd9f71c5922d1cea10df.tgz",
+    "ember-source": "~3.0.0-beta.5",
     "ember-source-channel-url": "^1.0.1",
     "ember-try": "^1.0.0-beta.1",
     "eslint-config-prettier": "^2.6.0",
@@ -86,4 +86,4 @@
   "ember-addon": {
     "configPath": "tests/dummy/config"
   }
-}
+}

yarn.lock

@@ -2822,9 +2822,9 @@ ember-source-channel-url@^1.0.1:
   dependencies:
     got "^8.0.1"
 
-ember-source@~3.0.0-beta.2:
-  version "3.0.0-beta.3"
-  resolved "https://registry.yarnpkg.com/ember-source/-/ember-source-3.0.0-beta.3.tgz#1f6dde5caaaceb49b09b5fafb5b0627692e2d56c"
+ember-source@~3.0.0-beta.5:
+  version "3.0.0-beta.6"
+  resolved "https://registry.yarnpkg.com/ember-source/-/ember-source-3.0.0-beta.6.tgz#e8042c1781de4f125993bb41b067cb32fc61c419"
   dependencies:
     broccoli-funnel "^2.0.1"
     broccoli-merge-trees "^2.0.0"
@@ -2833,7 +2833,6 @@ ember-source@~3.0.0-beta.2:
     ember-cli-normalize-entity-name "^1.0.0"
     ember-cli-path-utils "^1.0.0"
     ember-cli-string-utils "^1.1.0"
-    ember-cli-test-info "^1.0.0"
     ember-cli-valid-component-name "^1.0.0"
     ember-cli-version-checker "^2.1.0"
     ember-router-generator "^1.2.3"