rewrite tests to use async syntax + newer helpers and improve Node compatibility (#12)

* rewrite tests to use async syntax + newer helpers and improve Node compatibility

* update oldest Node version to 12, use newer CI images

* use js-test-helpers 2.1.1

Author: eli-darkly

.circleci/config.yml

@@ -29,11 +29,9 @@ jobs:
   oldest-long-term-support-release:
     <<: *node-template
     docker:
-      - image: circleci/node:6
-      - image: redis
+      - image: cimg/node:12.22
 
   current-release:
     <<: *node-template
     docker:
-      - image: circleci/node:latest
-      - image: redis
+      - image: cimg/node:current

package.json

@@ -32,7 +32,7 @@
   "devDependencies": {
     "buffer-from": "^1.1.1",
     "express": "^4.15.3",
-    "launchdarkly-js-test-helpers": "1.2.0",
+    "launchdarkly-js-test-helpers": "2.1.1",
     "mocha": "5.2.0",
     "nyc": "^15.0.0",
     "serve-static": "^1.12.3",