fix: use chain id in receivers

Author: ameeshaagrawal

src/notaries/native-bridge/ArbitrumReceiver.sol

@@ -32,7 +32,9 @@ contract ArbitrumReceiver is NativeBridgeNotary {
         address remoteTarget_,
         address inbox_
     ) NativeBridgeNotary(signatureVerifier_, chainSlug_, remoteTarget_) {
-        isL2 = (chainSlug_ == 42161 || chainSlug_ == 421613) ? true : false;
+        isL2 = (block.chainid == 42161 || block.chainid == 421613)
+            ? true
+            : false;
         inbox = IInbox(inbox_);
     }
 }

src/notaries/native-bridge/OptimismReceiver.sol

@@ -28,7 +28,7 @@ contract OptimismReceiver is NativeBridgeNotary {
         uint32 chainSlug_,
         address remoteTarget_
     ) NativeBridgeNotary(signatureVerifier_, chainSlug_, remoteTarget_) {
-        isL2 = (chainSlug_ == 10 || chainSlug_ == 420) ? true : false;
+        isL2 = (block.chainid == 10 || block.chainid == 420) ? true : false;
         OVM_L2_CROSS_DOMAIN_MESSENGER = ovmL2CrossDomainMessenger;
     }
 }

src/notaries/native-bridge/PolygonReceiver.sol

@@ -54,7 +54,7 @@ contract PolygonReceiver is NativeBridgeNotary, IFxMessageProcessor {
         uint32 chainSlug_,
         address remoteTarget_
     ) NativeBridgeNotary(signatureVerifier_, chainSlug_, remoteTarget_) {
-        isL2 = (chainSlug_ == 137 || chainSlug_ == 80001) ? true : false;
+        isL2 = (block.chainid == 137 || block.chainid == 80001) ? true : false;
         _fxRootSender = fxRootSender;
         _fxChild = fxChild;
     }