Add newline to warning by `mrb_warn()`
MODIFY
src/error.c
src/error.c
@@ -376,6 +376,7 @@ mrb_warn(mrb_state *mrb, const char *fmt, ...)
str = mrb_vformat(mrb, fmt, ap);
fputs("warning: ", stderr);
fwrite(RSTRING_PTR(str), RSTRING_LEN(str), 1, stderr);
+ putc('\n', stderr);
va_end(ap);
#endif
}

Add newline to warning by `mrb_warn()`