Fixed the drop option so that setting drop to false would result in no d...

...rop occuring.

Previously when using export to file and possibly export to database(Although I did not test this). The plugin would always drop the database. This pull request remedies this by modifying the use of 
```java
    if (drop) {
      schemaExport.drop(print, export);
    }
    schemaExport.create(print, export);
```
to
```java
    schemaExport.execute(print, export, false, !drop);
```

Rectifying the error.