txoo: compose env var set network not chain

- no need of using switch in entrypoint
- directly set the network instead of chain
Signed-off-by: Lakshya Singh <lakshay.singh1108@gmail.com>

docker-compose.regtest.yml

@@ -28,4 +28,5 @@ services:
     command:
       - -r http://rpcuser:VLSsigner1@bitcoind:38332
     environment:
-      - BITCOIN_CHAIN=regtest
+      - BITCOIN_NETWORK=regtest
+