fix: jest bug (facebook/create-react-app#6591)

    TypeError: Cannot assign to read only property 'Symbol(Symbol.toStringTag)' of object '#<process>'
      at exports.default (node_modules/jest-util/build/create_process_object.js:15:34)

fix:

Author: takeshi-hirosue

.travis.yml

@@ -4,6 +4,7 @@ language: node_js
 
 node_js:
   - 'stable'
+  - 'lts/*'
 dist: trusty
 sudo: false
 cache: yarn