ensure that module can be required in node without errors

see #1642

>We have this library bundled and running in an isomorphic application, but on the server nothing is ever called. It just needs to be bundled safely.

scripts/travis.sh

@@ -6,6 +6,9 @@ npm install
 
 if [ "${TRAVIS_MODE}" = "build" ]; then
 	npm run lint && npm run build
+  # check that hls.js doesn't error if requiring in node
+  # see https://github.com/video-dev/hls.js/pull/1642
+  node -e 'require("./" + require("./package.json").main)'
 elif [ "${TRAVIS_MODE}" = "unitTests" ]; then
 	npm run test:unit
 elif [ "${TRAVIS_MODE}" = "funcTests" ]; then