Debug Travis build failure

[mwood77]

Travis build fails during CI/CD run.
Link to build: https://travis-ci.org/github/MyBitFoundation/MyBit-Go.app/builds/773926702

Fails on command:

$ BUILD_URL=$(npx vercel --name app-mybit-io -t $NOW_PROD_TOKEN)
Error! option requires argument: -t (alias for --token)
The command "BUILD_URL=$(npx vercel --name app-mybit-io -t $NOW_PROD_TOKEN)" exited with 1.

Possible solution:
Vercel deployment/auth token missing from Travis environment variables.