This patch sets continuous deployment of playwright packages
from tip-of-tree. These packages are released under the "@next",
so it should be possible to install tip-of-tree version of Playwright
from NPM using
```
npm i playwright@next
```
A few technical details:
- This uses travis to drive deployments
- This deploys from master and only if all browsers pass all tests on linux
- This is an attempt to deploy just two packages: `playwright-core` and `playwright-firefox`. If this works out, I'll follow-up with other packages as well