Date datetype is written as text

Hi, 

I am seeing my date columns are written as characters in to database. In case if i retrieve the data from database, it still reads that as character.  

```
> dbDataType(RMySQL::MySQL(), Sys.Date)
[1] "text"
```

And my RMySQL version is this - `Package RMySQL version 0.10.11` . From my understanding, it seems this was fixed on this - #17 