Failures with resolution of `pwa-helpers`

[shanehandley]

The following errors are reported when hitting the application in the browser after executing npm start.

The browser console reports:

Loading failed for the <script> with source “http://127.0.0.1:8081/src/components/pwa-helpers/connect-mixin.js”. 127.0.0.1:8081:1
Loading failed for the <script> with source “http://127.0.0.1:8081/src/components/pwa-helpers/router.js”. 127.0.0.1:8081:1
Loading failed for the <script> with source “http://127.0.0.1:8081/src/components/pwa-helpers/metadata.js”. 127.0.0.1:8081:1
Loading failed for the <script> with source “http://127.0.0.1:8081/src/components/pwa-helpers/network.js”. 127.0.0.1:8081:1
Loading failed for the <script> with source “http://127.0.0.1:8081/src/pwa-helpers/lazy-reducer-enhancer.js”. 127.0.0.1:8081:1
[Show/hide message details.] TypeError: Failed to fetch http://127.0.0.1:8081/src/components/pwa-helpers/connect-mixin.js 127.0.0.1:8081:111:496 

The node console reports:

Could not resolve module specifier "pwa-helpers/connect-mixin.js" in file "/Users/.../www/flash-cards/src/components/my-app.js".
Could not resolve module specifier "pwa-helpers/router.js" in file "/Users/.../www/flash-cards/src/components/my-app.js".
Could not resolve module specifier "pwa-helpers/network.js" in file "/Users/.../www/flash-cards/src/components/my-app.js".
Could not resolve module specifier "pwa-helpers/metadata.js" in file "/Users/.../www/flash-cards/src/components/my-app.js".
Could not resolve module specifier "pwa-helpers/lazy-reducer-enhancer.js" in file "/Users/.../www/flash-cards/src/store.js"

I've tried re-installing pwa-helpers to no avail. Interestingly, the package.json reference differs after manual installation:

diff --git a/package.json b/package.json
index b3c76b1..00de8ef 100644
--- a/package.json
+++ b/package.json
@@ -25,7 +25,7 @@
   "dependencies": {
     "@polymer/lit-element": "^0.5.2",
     "@webcomponents/webcomponentsjs": "^2.0.2",
-    "pwa-helpers": "Polymer/pwa-helpers",
+    "pwa-helpers": "github:Polymer/pwa-helpers",
     "redux": "^3.7.2",
     "redux-thunk": "^2.2.0",
     "reselect": "^3.0.1"

$ node -v && npm -v
v8.11.3
6.4.1

Thanks. Let me know if I can provide any additional information.