change ws/http substitution to first occurrence only (#145)

Author: Roberto Bayardo

op-node-entrypoint

@@ -7,7 +7,7 @@ if [[ -z "$OP_NODE_NETWORK" ]]; then
 fi
 
 # wait until local geth comes up (authed so will return 401 without token)
-until [ "$(curl -s -w '%{http_code}' -o /dev/null "${OP_NODE_L2_ENGINE_RPC//ws/http}")" -eq 401 ]; do
+until [ "$(curl -s -w '%{http_code}' -o /dev/null "${OP_NODE_L2_ENGINE_RPC/ws/http}")" -eq 401 ]; do
   echo "waiting for geth to be ready"
   sleep 5
 done