message: Collect memories into Option<Memory> instead of Vec
diff: @@ -301,13 +301,13 @@ impl<A: BackendApi, S: Storage, Q: Querier> Environment<A, S, Q> {
  pub fn memory(&self) -> Memory {
  self.with_wasmer_instance(|instance| {
  - let mut memories: Vec<Memory> = instance
  + let first: Option<Memory> = instance
  .exports
  .iter()
  .memories()
  - .map(|pair| pair.1.clone())
  - .collect();
  - let memory = memories.pop().unwrap();
  + .next()
  + .map(|pair| pair.1.clone());
  + let memory = first.unwrap();
  Ok(memory)
  })
  .expect("Wasmer instance is not set. This is a bug in the lifecycle.")
  