change tests to use nyc

Author: idantovi

.travis.yml

@@ -3,5 +3,9 @@ node_js:
   - "6"
   - "8"
   - "node"
-script: "npm run test-travis"
-after_success: 'npm run coveralls'
+script: "npm test"
+after_success: >
+  node_version=$(node -v);
+  if  [ ${node_version:1:1} -ne 6 ]; then
+     npm run coveralls
+  fi