docs: Update old link to networkHarness framework (#919)

docs/code_contribution_guidelines.md

@@ -160,7 +160,7 @@ A quick summary of test practices follows:
   be accompanied by unit tests exercising the new or changed behavior.
 - Changes to behavior within the daemon's interaction with the P2P protocol,
   or RPC's will need to be accompanied by integration tests which use the
-  [`networkHarness`framework](https://github.com/lightningnetwork/lnd/blob/master/networktest.go)
+  [`networkHarness`framework](https://github.com/lightningnetwork/lnd/blob/master/lntest/harness.go)
   contained within `lnd`. For example integration tests, see
   [`lnd_test.go`](https://github.com/lightningnetwork/lnd/blob/master/lnd_test.go#L181).