Removing misleading info on Contracts

[Udiknedormin]

Both examples of Contracts errors to be removed from README:

• the {.compiletime.} example was buggy to begin with. The error came from not using "static" when calling compile-time-only proc, which will always raise the same error in any Nim code, Contracts, Contra or just a plain proc. Contracts itself handles {.compiletime.} just fine and has been tested to do so.
• the JS and NimScript target examples have been solved successfully, they do not error with the newest versions of Contracts (even though NimScript cannot support all of Contracts' other features)