fix known account class for braavos

[0xcoburn]

update known account class

[xJonathanLEI]

Thanks for the PR! I'm not sure we should add a AccountVariantType variant for this though? These variants exist only to deal with account classes with different interfaces so that they need to be treated differently when fetching. If the new Braavos class exposes the same interface (as far as our use of it is concerned, of course), we can just add the hash.

I will have to check which is the case though.

[xJonathanLEI]

Branch does not compile.

[xJonathanLEI]

Superseded by d2c3342.