Update Snowball submodules to current version

[molesinski]

I've been using this Nuget package as a dependency for my upcoming in memory search library, but noticed that the current version of generated stemmers causes significant memory allocations. While directly embedding current Snowball generated stemmers results in no allocation stemming. This is due to the fact, that C# code generation has been improved over last 2 years.

Can you please update submodules to current version ? I would very much prefer taking dependency on libstemmer.net, rather than embedding generated stemmers.