Missing feature flag for tokio in macros crate

[IsaacTru]

When using the runtime-tokio and macros features, a compile time error is generated:

error[E0599]: no method named `threaded_scheduler` found for type `tokio::runtime::builder::Builder` in the current scope
  --> /home/isaac/.cargo/registry/src/github.com-1ecc6299db9ec823/sqlx-macros-0.2.1/src/lib.rs:32:14
   |
32 |             .threaded_scheduler()
   |              ^^^^^^^^^^^^^^^^^^ method not found in `tokio::runtime::builder::Builder`

A work-around is to include the following dependency in Cargo.toml:

tokio = { version = "0.2.9", default-features = false, features = [ "rt-threaded" ] }

[mehcode]

Fixed and released as v0.2.2