don't attempt to link contract if it's not in the code

lib/contracts/deploy.js

@@ -109,6 +109,9 @@ class Deploy {
           deployedAddress = deployedAddress.substr(2);
         }
         let linkReference = '__' + filename + ":" + contractObj.className;
+        if (contractCode.indexOf(linkReference) < 0) {
+          continue;
+        }
         let toReplace = linkReference + "_".repeat(40 - linkReference.length);
         contractCode = contractCode.replace(new RegExp(toReplace, "g"), deployedAddress);
       }