Add codecov.io configuration to travis file

.travis.yml

@@ -1,7 +1,15 @@
 language: go
-script: go test -v -race ./...
 
 go:
   - 1.5
   - 1.6
   - tip
+
+before_install:
+  - go get -t -v ./...
+
+script: go test -v -race -coverprofile=coverage.txt -covermode=atomic .
+
+after_success:
+  - bash <(curl -s https://codecov.io/bash)
+