Enable Travis CI.

.travis.yml

+sudo: false
+
+
+language: go
+go:
+  - 'tip'
+  
+install:
+  - go get github.com/whyrusleeping/gx
+  - go get github.com/whyrusleeping/gx-go
+  - gx install --global
+script:
+  - gx test -v -race -coverprofile=coverage.txt -covermode=atomic .
+  
+after_success:
+  - bash <(curl -s https://codecov.io/bash)
+
+cache:
+  directories:
+    - $GOPATH/src/gx
+
+notifications:
+email: false
+