make errors more descriptive

Author: YaroShkvorets

packages/cli/src/command-helpers/contracts.ts

@@ -248,7 +248,7 @@ export class ContractService {
       }
     }
 
-    throw new Error(`JSON-RPC is unreachable`);
+    throw new Error(`No implementation address found`);
   }
 
   private async fetchTransactionByHash(networkId: string, txHash: string) {
@@ -279,6 +279,6 @@ export class ContractService {
       }
     }
 
-    throw new Error(`JSON-RPC is unreachable`);
+    throw new Error(`Failed to fetch tx ${txHash}`);
   }
 }