Demo readmes should be of the template `npm run-script test-demo -- demos/<FOLDER>/`, but it is appended with `test.js`

[AbhinavMir]

Since run-test.sh already has the following line, ./node_modules/.bin/mocha --full-trace --reporter spec ${TESTDIR}/test.js, writing a test line such as in this readme seems redundant. I could be wrong, but running just npm run-script test-demo -- demos/sum works for me, while npm run-script test-demo -- demos/sum/test.js errors out.

Could fix this in a PR, if this is a legit issue!

Cheers.