message: add feature gate on import
diff: @@ -15,6 +15,7 @@ use wasmer::*;
  use wasmer_emscripten;
  use wasmer_runtime::cache::{Cache as BaseCache, FileSystemCache, WasmHash, WASMER_VERSION_HASH};
  use wasmer_runtime_core::backend::CompilerConfig;
  +#[cfg(feature = "wasi")]
  use wasmer_wasi;
  #[derive(Debug, StructOpt)]
  