v0.1.x lint fix, MSRV 1.28.0 updates (#1451)

* use dyn Trait syntax where appropriate

recent rust nightly started warning that not using `dyn` was
deprecated. This requires MSRV 1.27.0+.

* rustfmt fallout from dyn additions

* stop explicit allow of rust_2018_idioms

* more dyn Trait syntax

* drop tokio-macros from 0.1.x workspace

Since tokio-macros specifies an edition=2018, we would otherwise
require MSRV 1.31.0 to build/test it. And tokio-macros isn't used with
tokio 0.1.x.

* reactor: narrow tokio-io-pool dev dep to 0.1.4

Since 0.1.5-6 is now a edition=2018 crate, which has effective MSRV
1.31.0.

* narrow tempfile dev-dep to avoid MSRV bump

tempfile 3.1.0 pulls in rand 0.7.0 and is MSRV 1.32.0

* narrow flate2 dev-dep to avoid MSRV bump

flate2 1.0.10-11 have MSRV 1.34.0.

github refs: alexcrichton/flate2-rs#207

* fs: drop deprecated tempdir crate use in tests

In particular because it pulls in old rand duplicates. Replace use
with tempfile::tempdir() which has been available since tempfile
3.0.0.

backport-of: #1312

* increase CI MSRV to 1.28.0

tokio-timer/src/clock/clock.rs

@@ -17,7 +17,7 @@ use std::time::Instant;
 /// [`Instant::now`]: https://doc.rust-lang.org/std/time/struct.Instant.html#method.now
 #[derive(Default, Clone)]
 pub struct Clock {
-    now: Option<Arc<Now>>,
+    now: Option<Arc<dyn Now>>,
 }
 
 thread_local! {

tokio-timer/src/throttle.rs

@@ -158,7 +158,7 @@ impl<T: StdError + 'static> StdError for ThrottleError<T> {
     // FIXME(taiki-e): When the minimum support version of tokio reaches Rust 1.30,
     // replace this with Error::source.
     #[allow(deprecated)]
-    fn cause(&self) -> Option<&StdError> {
+    fn cause(&self) -> Option<&dyn StdError> {
         match self.0 {
             Either::A(ref err) => Some(err),
             Either::B(ref err) => Some(err),

tokio-timer/src/timer/mod.rs

@@ -162,7 +162,7 @@ pub(crate) struct Inner {
     process: AtomicStack,
 
     /// Unparks the timer thread.
-    unpark: Box<Unpark>,
+    unpark: Box<dyn Unpark>,
 }
 
 /// Maximum number of timeouts the system can handle concurrently.
@@ -426,7 +426,7 @@ impl<T, N> Drop for Timer<T, N> {
 // ===== impl Inner =====
 
 impl Inner {
-    fn new(start: Instant, unpark: Box<Unpark>) -> Inner {
+    fn new(start: Instant, unpark: Box<dyn Unpark>) -> Inner {
         Inner {
             num: AtomicUsize::new(0),
             elapsed: AtomicU64::new(0),