Hide credentials from the code, use env variables instead.

[tp-cai]

Just an idea and I think it would be helpful since generally, we don't want to hard code our credentials to the code. Right now I have replaced the value of DB credentials in Constant.scala which holds me back from pushing the code to the cloud.

[patsonluk]

@tp-cai sorry probably have missed this, The db credentials can be provided via config. is that good enough? https://github.com/patsonluk/airline/blob/master/airline-data/src/main/scala/com/patson/data/Constants.scala#L190