Request: Fix 'warning: trait objects without an explicit `dyn` are deprecated'

[phrohdoh]

When building dynomite@0.5.1 with the 2018 edition of Rust I get the following warning.

warning: trait objects without an explicit `dyn` are deprecated
  --> dynomite/src/ext.rs:15:33
   |
15 | type DynomiteStream<I, E> = Box<Stream<Item = I, Error = RusotoError<E>> + Send>;
   |                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: use `dyn`: `dyn Stream<Item = I, Error = RusotoError<E>> + Send`
   |
   = note: `#[warn(bare_trait_objects)]` on by default

Getting this fixed would be nice.