feat: setup continuous deployment (#1159)

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

.travis.yml

@@ -29,10 +29,32 @@ cache:
   directories:
   - node_modules
 script:
-  - "npm run lint"
-  - "xvfb-run --auto-servernum npm run ctest"
-  - "xvfb-run --auto-servernum npm run ftest"
-  - "xvfb-run --auto-servernum npm run wtest"
+- npm run lint
+- xvfb-run --auto-servernum npm run ctest
+- xvfb-run --auto-servernum npm run ftest
+- xvfb-run --auto-servernum npm run wtest
 jobs:
   include:
-    - node_js: "12"
+  - node_js: '12'
+
+before_deploy: npm run apply-next-version
+deploy:
+  matrix:
+  - provider: npm
+    edge: true
+    email: aslushnikov@gmail.com
+    src: '.'
+    on:
+      branch: master
+    skip_cleanup: true
+    tag: next
+  - provider: npm
+    edge: true
+    email: aslushnikov@gmail.com
+    src: './packages/playwright-firefox'
+    on:
+      branch: master
+    skip_cleanup: true
+    tag: next
+  api_key:
+    secure: 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

utils/apply_next_version.js

@@ -21,5 +21,6 @@ if (dashIndex !== -1)
   version = version.substring(0, dashIndex);
 version += '-next.' + Date.now();
 console.log('Setting version to ' + version);
-package.version = version;
-fs.writeFileSync(path.join(__dirname, '..', 'package.json'), JSON.stringify(package, undefined, 2) + '\n');
+
+execSync(`npm --no-git-tag-version version ${version}`);
+