Conversions: Remove the version number from import.

- Convert::Pluggable version is already set in dist.ini
- Getting an error on DuckPAN because of it.

```
Invalid version format (non-numeric data) at /opt/perlbrew/perls/perl-5.16.3/lib/site_perl/5.16.3/Exporter/Heavy.pm line 120.
BEGIN failed--compilation aborted at lib/DDG/Goodie/Conversions.pm line 8.
Compilation failed in require at /usr/local/ddg.cpan/perl5/lib/perl5/App/DuckPAN/Cmd.pm line 19.
```