Add requiredMessageLength method to BasicHomeBridge contract

contracts/libraries/Message.sol

@@ -66,7 +66,7 @@ library Message {
         return _msg.length == requiredMessageLength();
     }
 
-    function requiredMessageLength() public pure returns(uint256) {
+    function requiredMessageLength() internal pure returns(uint256) {
         return 104;
     }
 

contracts/upgradeable_contracts/BasicHomeBridge.sol

@@ -141,5 +141,7 @@ contract BasicHomeBridge is EternalStorage, Validatable {
         return uintStorage[keccak256(abi.encodePacked("numMessagesSigned", _message))];
     }
 
-
+    function requiredMessageLength() public pure returns(uint256) {
+        return Message.requiredMessageLength();
+    }
 }