Improve error message when calling bundlingComplete

[digitalsadhu]

Improve the printing out off the feedHashes array.

{"@version":1,"@timestamp":"2018-04-09T12:37:26.594Z","level":"WARN","message":"readiness check failed","throwable":"AssertionError [ERR_ASSERTION]: Expected all entries in array 'feedHashes' to be strings when calling 'bundlingComplete(feedHashes)'. Instead 'feedHashes' was ,https://widget.messaging.schibsted.io/faast.min.js\n    at Client.bundlingComplete (/home/node/src/node_modules/@asset-pipe/client/lib/main.js:433:9)\n    at Object.ready (/home/node/src/lib/server-impl.js:65:35)\n    at app.get (/home/node/src/node_modules/@finn-no/health-checks/lib/index.js:64:32)\n    at Layer.handle [as handle_request] (/home/node/src/node_modules/express/lib/router/layer.js:
95:5)\n    at next (/home/node/src/node_modules/express/lib/router/route.js:137:13)\n    at Route.dispatch (/home/node/src/node_modules/express/lib/router/route.js:112:3)\n    at Layer.handle [as handle_request] (/home/node/src/node_modules/express/lib/router/layer.js:95:5)\n    at /home/node/src/node_modules/express/lib/router/index.js:281:22\n    at Function.process_params (/home/node/src/node_modules/express/lib/router/index.js:335:12)\n    at next (/home/node/src/node_modules/express/lib/router/index.js:275:10)\n    at expressInit (/home/node/src/node_modules/express/lib/middleware/init.js:40:5)\n    at Layer.handle [as handle_request] (/home/node/src/node_modules
/express/lib/router/layer.js:95:5)\n    at trim_prefix (/home/node/src/node_modules/express/lib/router/index.js:317:13)\n    at /home/node/src/node_modules/express/lib/router/index.js:284:7\n    at Function.process_params (/home/node/src/node_modules/express/lib/router/index.js:335:12)\n    at next (/home/node/src/node_modules/express/lib/router/index.js:275:10)","LocationInfo":{"file":"/home/node/src/lib/server-impl.js","module":"finnbox-www-layout-server","method":"Client.bundlingComplete","line":433}}

feedHashes with null or undefined first value results in something like this:

Instead 'feedHashes' was ,https://widget.messaging.schibsted.io/faast.min.js