chore: change default lint level to warning and deny warnings in CI (#1416)

tokio-codec/tests/codecs.rs

@@ -1,4 +1,4 @@
-#![deny(warnings, rust_2018_idioms)]
+#![warn(rust_2018_idioms)]
 
 use bytes::{BufMut, Bytes, BytesMut};
 use tokio_codec::{BytesCodec, Decoder, Encoder, LinesCodec};

tokio-codec/tests/framed.rs

@@ -1,5 +1,5 @@
 #![feature(async_await)]
-#![deny(warnings, rust_2018_idioms)]
+#![warn(rust_2018_idioms)]
 
 use tokio::prelude::*;
 use tokio_codec::{Decoder, Encoder, Framed, FramedParts};

tokio-codec/tests/framed_read.rs

@@ -1,5 +1,5 @@
 #![feature(async_await)]
-#![deny(warnings, rust_2018_idioms)]
+#![warn(rust_2018_idioms)]
 
 use tokio::prelude::*;
 use tokio_codec::{Decoder, FramedRead};

tokio-codec/tests/framed_write.rs

@@ -1,4 +1,4 @@
-#![deny(warnings, rust_2018_idioms)]
+#![warn(rust_2018_idioms)]
 
 use tokio_codec::{Encoder, FramedWrite};
 use tokio_io::AsyncWrite;

tokio-codec/tests/length_delimited.rs

@@ -1,4 +1,4 @@
-#![deny(warnings, rust_2018_idioms)]
+#![warn(rust_2018_idioms)]
 
 use tokio::codec::*;
 use tokio::io::{AsyncRead, AsyncWrite};