Use correct hashing program

src/restore.ts

@@ -82,7 +82,7 @@ async function run(): Promise<void> {
                 cacheEntry?.archiveLocation,
                 archivePath
             );
-            exec("md5", [archivePath]);
+            await exec(`md5sum`, [archivePath]);
 
             const archiveFileSize = utils.getArchiveFileSize(archivePath);
             core.info(

src/save.ts

@@ -52,7 +52,7 @@ async function run(): Promise<void> {
             "cache.tgz"
         );
         core.debug(`Archive Path: ${archivePath}`);
-        exec("md5", [archivePath]);
+        await exec(`md5sum`, [archivePath]);
 
         // http://man7.org/linux/man-pages/man1/tar.1.html
         // tar [-options] <name of the tar archive> [files or directories which to add into archive]