Even though the mintable tokens are not upgradable, this
commit adds semver to them in case we change the implementations
down the road and then update the factories to deploy the new
versions. I do think it would be nice to know what version
different mintable tokens are on, in case we decide to add
functionality to the mintable tokens.

This will make it very easy to know what version the mintable
tokens are at, in case newer mintable tokens have different
functionality in some way.