fix: mrbgems\mruby-string-ext\src\string.c(49): warning C4244: '=': conversion...

fix: mrbgems\mruby-string-ext\src\string.c(49): warning C4244: '=': conversion from 'mrb_int' to 'int', possible loss of data

mrbgems/mruby-string-ext/src/string.c

@@ -44,7 +44,7 @@ mrb_str_byteslice(mrb_state *mrb, mrb_value str)
 {
   mrb_value a1;
   mrb_int len;
-  int argc;
+  mrb_int argc;
 
   argc = mrb_get_args(mrb, "o|i", &a1, &len);
   if (argc == 2) {