cmd: start linting fixes.

cmd/cruntar/main.go

@@ -262,11 +262,11 @@ func main() {
 
 	tfr := tar.NewReader(r)
 	for {
-		hdr, err := tfr.Next()
-		if err == io.EOF {
-			break
-		}
-		die.If(err)
+  hdr, err := tfr.Next()
+  if errors.Is(err, io.EOF) {
+      break
+  }
+  die.If(err)
 
 		err = processFile(tfr, hdr, top)
 		die.If(err)