setup postgres on travis

.travis.yml

@@ -1,9 +1,13 @@
 language: go
 go:
-- 1.4.2
+  - 1.4.2
+addons:
+  postgresql: "9.4"
+env:
+  - DATABASE_URL=postgres://postgres@localhost/?sslmode=disable
 before_install:
   - go get github.com/axw/gocov/gocov
   - go get github.com/mattn/goveralls
   - if ! go get code.google.com/p/go.tools/cmd/cover; then go get golang.org/x/tools/cmd/cover; fi
 script:
-    - $HOME/gopath/bin/goveralls -service=travis-ci
+  - $HOME/gopath/bin/goveralls -service=travis-ci