Fix postgresql93 sample credentials config.
Fix postgresql93 sample credentials config.

Fixes #42

cloudfoundry-community/cf-containers-broker,tproot/cf-containers-broker,cf-platform-eng/cf-containers-broker,cf-platform-eng/cf-containers-broker,cf-platform-eng/cf-containers-broker,cloudfoundry-community/cf-containers-broker,tproot/cf-containers-broker,cloudfoundry-community/cf-containers-broker,tproot/cf-containers-broker