fix: mrbgems\mruby-string-ext\src\string.c(30): warning C4244: '=': conversion...

fix: mrbgems\mruby-string-ext\src\string.c(30): warning C4244: '=': conversion from 'mrb_int' to 'long', possible loss of data

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

@@ -23,7 +23,7 @@ static mrb_value
 mrb_str_setbyte(mrb_state *mrb, mrb_value str)
 {
   mrb_int pos, byte;
-  long len;
+  mrb_int len;
 
   mrb_get_args(mrb, "ii", &pos, &byte);