Fix travis config

.travis.yml

@@ -1,16 +1,12 @@
 sudo: false
 language: node_js
 cache:
-  yarn: true
   directories:
     - node_modules
 node_js:
-- '6'
+- '8'
 script:
-# Unfortunately flow falls over when a dep exists in peer deps and others. :(
-# @see https://github.com/flowtype/flow-typed/issues/528
-#- yarn run flow:defs
-- yarn run check
+- npm run check
 after_success:
 # Deploy code coverage report to codecov.io
-- yarn run test:coverage:deploy
+- npm run test:coverage:deploy