Added coverage

.travis.yml

@@ -1,4 +1,12 @@
 language: go
 go:
   - tip
-go_import_path: go.mozilla.org/sops/
+go_import_path: go.mozilla.org/sops/
+before_intall:
+  - go get -t -v ./...
+
+script:
+  - go test -coverprofile=coverage.txt -covermode=atomic
+
+after_success:
+  - bash <(curl -s https://codecov.io/bash)