Add chai-as-promised as a devDependency.

This satisfies `chai@4`'s `peerDependencies` requirement for `chai-as-promised`.

Author: Robert Jackson

package.json

@@ -43,6 +43,7 @@
     "broccoli-asset-rev": "^2.4.2",
     "broccoli-test-helper": "^1.1.0",
     "chai": "^4.0.0",
+    "chai-as-promised": "^7.1.1",
     "co": "^4.6.0",
     "ember-cli": "2.14.1",
     "ember-cli-babel": "^6.4.1",

yarn.lock

@@ -1265,6 +1265,12 @@ chai-as-promised@^6.0.0:
   dependencies:
     check-error "^1.0.2"
 
+chai-as-promised@^7.1.1:
+  version "7.1.1"
+  resolved "https://registry.yarnpkg.com/chai-as-promised/-/chai-as-promised-7.1.1.tgz#08645d825deb8696ee61725dbf590c012eb00ca0"
+  dependencies:
+    check-error "^1.0.2"
+
 chai-files@^1.0.0, chai-files@^1.1.0:
   version "1.4.0"
   resolved "https://registry.yarnpkg.com/chai-files/-/chai-files-1.4.0.tgz#0e25610fadc551b1eae79c2f4ee79faf2f842296"