Use codecov bash uploader (#249)

This works in Travis CI windows because the build is run under git-bash.

.travis.yml

@@ -15,7 +15,7 @@ install:
 script:
   - npm test
 after_success:
-  - ./node_modules/.bin/codecov
+  - bash <(curl -s https://codecov.io/bash)
 # safelist (prevent double builds in PRs)
 branches:
   only: