Update 01_counter.sol

xanpena · web-flow · commit 3cbf21e38c94 · 2022-01-15T09:01:28.000+01:00
diff --git a/01_counter.sol b/01_counter.sol
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-3.0
 pragma solidity >=0.7.0 <0.9.0;
 
 contract Counter {
