Correct default names of .sol files

Author: timothymcmackin

docs/tutorials/marketpulse/backend.md

@@ -5,7 +5,7 @@ For more information about Solidity, see https://docs.soliditylang.org.
 
 Follow these steps to set up a Solidity smart contract:
 
-1. Remove the default Solidity smart contract `Lock.sol` in the `./contracts` folder.
+1. Remove the default Solidity smart contract files `Counter.sol` and `Counter.t.sol` in the `./contracts` folder.
 
 1. Create a new file named `Marketpulse.sol` in the `./contracts` folder.