Fix a mismatching size warning
Fix a mismatching size warning

```
ext/mysql2/result.c:259:55: warning: format specifies type 'long' but the argument has type 'int' [-Wformat]
        rb_field_type = rb_sprintf("decimal(%ld,%d)", precision, field->decimals);
```

jeremy/mysql2,sodabrew/mysql2,sodabrew/mysql2,brianmario/mysql2,brianmario/mysql2,brianmario/mysql2,sodabrew/mysql2,jeremy/mysql2,jeremy/mysql2