don't replace frozen strings

[bbonislawski]

In rails 5.2 these strings are frozen and you cannot replace them. Overrwriting constants generates warnining but I cannot see how to do it better at the moment

[coveralls]

Coverage remained the same at 100.0% when pulling d98a019 on spark-solutions:master into 00af59f on bwillis:master.

[bbonislawski]

@bwillis Versioncake doesn't work with rails 5.2. This is fix, can you look into that?

[bwillis]

Thanks for the fix! I think this is good enough for now, I'll get this pulled in and released. Sorry for the delay! 🌈