Update travis CI builder to also run node 10

I'm not sure if this will work first-try, since it's been a while since I've touched Travis-CI. But lets hope!

.travis.yml

@@ -1,7 +1,9 @@
 language: node_js
 node_js:
     - "8"
+    - "10"
+
 script:
     - ./node_modules/.bin/istanbul cover --report lcov node_modules/.bin/_mocha test/
 after_success:
-    - cat ./coverage/lcov.info | ./node_modules/coveralls/bin/coveralls.js
+    - cat ./coverage/lcov.info | ./node_modules/coveralls/bin/coveralls.js