Added Address.sol for isContract checks to contracts-utils package

contracts/erc1155/compiler.json

@@ -25,7 +25,6 @@
         "src/MixinNonFungibleToken.sol",
         "src/interfaces/IERC1155Mintable.sol",
         "src/interfaces/IERC1155Receiver.sol",
-        "src/interfaces/IERC1155.sol",
-        "src/utils/Address.sol"
+        "src/interfaces/IERC1155.sol"
     ]
 }

contracts/erc1155/contracts/src/ERC1155.sol

@@ -19,7 +19,7 @@
 pragma solidity ^0.5.3;
 
 import "@0x/contracts-utils/contracts/src/SafeMath.sol";
-import "./utils/Address.sol";
+import "@0x/contracts-utils/contracts/src/Address.sol";
 import "./interfaces/IERC1155.sol";
 import "./interfaces/IERC1155Receiver.sol";
 import "./MixinNonFungibleToken.sol";

contracts/utils/CHANGELOG.json

@@ -13,6 +13,10 @@
             {
                 "note": "Upgrade contracts to Solidity 0.5.5",
                 "pr": 1682
+            },
+            {
+                "note": "Added Address.sol with test for whether or not an address is a contract",
+                "pr": 1657
             }
         ]
     },

contracts/utils/compiler.json

@@ -23,6 +23,7 @@
         }
     },
     "contracts": [
+        "src/Address.sol",
         "src/LibBytes.sol",
         "src/Ownable.sol",
         "src/ReentrancyGuard.sol",