RTT example - allow empty lines too

[fanoush]

It is typical to just press enter to see if console input is working, I was very confused that nothing happens so connected to my device via UART to produce some output to RTT, and only after I found it working I had an idea to actually type some text before pressing enter.

BTW I could not test it but hopefully it works, I cloned repo and set up github pages but when trying at https://fanoush.github.io/dapjs/examples/rtt/web.html the page gets 404 on https://fanoush.github.io/dapjs/dist/dap.umd.js Not sure how I should put stuff to "dist"

EDIT: now I tested it by committing directly to my gh-pages branch and it seems to work