fix dynamic link for wasmer-type 2.2.1

[loloicci]

If we use wasmer-type 2.2.1 with dynamic_link macro following error is issued

error[E0308]: mismatched types
  --> src/contract.rs:16:1
   |
16 | #[dynamic_link(NumberContract)]
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected slice, found struct `std::vec::Vec`                                    
   |
   = note: expected reference `&[wasmer_types::types::ExportType<wasmer_types::types::FunctionType>]`          
              found reference `&std::vec::Vec<ExportType<FunctionType>>`
   = note: this error originates in the attribute macro `dynamic_link` (in Nightly builds, run with -Z macro-backtrace for more info)

[loloicci]

solved via #261