Prepare to release (puppeteer#532)

- add node6-transform to .npmignore
- dump node version in sanity test

Author: aslushnikov

.npmignore

@@ -4,6 +4,7 @@ third_party/phantomjs/
 phantom_shim
 # exclude all tests
 test
+utils/node6-transform
 
 # repeats from .gitignore
 node_modules

test/sanity.js

@@ -14,6 +14,8 @@
  * limitations under the License.
  */
 
+console.log(process.version);
+
 describe('Puppeteer Sanity', function() {
   it('should not be insane', function(done) {
     const puppeteer = require('..');