Update node-sass so tests pass on Node 12 (#76)

thanks for your contribution!

Author: dmellstrom

.travis.yml

@@ -1,9 +1,7 @@
 language: node_js
 node_js:
-  - "11"
+  - "12"
   - "10"
-  - "9"
   - "8"
-  - "7"
   - "6"
 after_script: "cat ./.coverage/lcov.info | ./node_modules/coveralls/bin/coveralls.js"