Fix db path on normal run.

[marcio-diaz]

This fixes the following error.

substrate-master git:(master) ✗ ./target/debug/substrate --dev            
2019-11-30 18:02:18 Running in --dev mode, RPC CORS has been disabled.
2019-11-30 18:02:18 Substrate Node
2019-11-30 18:02:18   version 2.0.0-ccd72addd-x86_64-linux-gnu
2019-11-30 18:02:18   by Parity Technologies, 2017-2019
2019-11-30 18:02:18 Chain specification: Development
2019-11-30 18:02:18 Node name: guarded-science-6820
2019-11-30 18:02:18 Roles: AUTHORITY
Error: Service(Client(Backend("IO error: No such file or directoryWhile mkdir if missing: No such file or directory")))

The function called contains the replaced ones and adds the path.

[bkchr]

I hope that we now have it xD 👍