Remove lts/carbon support

End-of-life: 2019-12-31 (https://github.com/nodejs/Release#end-of-life-releases)

Dependencies requiring at least lts/dubnium:
- ava: https://github.com/avajs/ava
- husky: https://github.com/typicode/husky

Author: stovmascript

.travis.yml

@@ -4,5 +4,5 @@ os:
 language: node_js
 node_js:
   - "lts/*"
-  - "lts/carbon"
+  - "lts/dubnium"
   - "node"