make DataGroup12 class public

[recp]

Hello, thanks for your great work,

The DataGroup12 seems to be internal and it cannot be accessed outside the library:

if let dg12 = pass.dataGroupsRead[.DG12] as? DataGroup12 {
  /* get dg12.dateOfIssue */
}

this PR makes it public, thanks

[Jeroenbb94]

+1 to merge this. This was changed in 1.1.8 to internal, it is public on 2.0.0 and on 1.1.7

[AndyQ]

Merged - thanks!