Remove #![feature(futures_api)] (#2)

* Remove #![feature(futures_api)]

* Change CI config to build on beta

* Fix clippy error/warning

Author: taiki-e

Diff for: .travis.yml

@@ -1,13 +1,13 @@
 language: rust
 rust:
-  - stable
+  - beta
 
 before_script: |
   rustup component add rustfmt-preview &&
   rustup component add clippy-preview
 script: |
   cargo fmt -- --check &&
-  cargo clippy -- -D clippy &&
+  cargo clippy -- -D clippy::all &&
   cargo build --verbose &&
   cargo test  --verbose
 cache: cargo

Diff for: README.md

@@ -11,8 +11,6 @@ Async datagram traits.
 ## Examples
 __Basic usage__
 ```rust
-#![feature(futures_api)]
-
 use async_datagram::AsyncDatagram;
 use std::task::{Context, Poll};
 use std::pin::Pin;

Diff for: src/lib.rs

@@ -8,8 +8,6 @@
 //! ## Example
 //!
 //! ```rust
-//! #![feature(futures_api)]
-//!
 //! use async_datagram::AsyncDatagram;
 //! use std::task::{Context, Poll};
 //! use std::pin::Pin;
@@ -40,8 +38,6 @@
 //! }
 //! ```
 
-#![feature(futures_api)]
-
 use std::pin::Pin;
 use std::task::{Context, Poll};
 
@@ -70,6 +66,7 @@ pub trait AsyncDatagram {
   ///
   /// On success, returns the number of bytes read and the target from whence
   /// the data came.
+  #[allow(clippy::type_complexity)]
   fn poll_recv_from(
     self: Pin<&mut Self>,
     cx: &mut Context<'_>,

Diff for: tests/test.rs

@@ -0,0 +1 @@
+