Add codecov support

Author: Octounit

.travis.yml

@@ -8,4 +8,8 @@ install:
 
 script:
   - go build ./...
-  - go test -v
+  - go test -v
+  - go test -race -coverprofile=coverage.txt -covermode=atomic
+
+after_success:
+  - bash <(curl -s https://codecov.io/bash)