Migrate to 2018 edition

Signed-off-by: koushiro <koushiro.cqx@gmail.com>

Cargo.toml

@@ -9,6 +9,7 @@ keywords = ["time", "human", "human-friendly", "parser", "duration"]
 homepage = "https://github.com/tailhook/humantime"
 documentation = "https://docs.rs/humantime"
 version = "1.3.0"
+edition = "2018"
 authors = ["Paul Colomiets <paul@colomiets.name>"]
 categories = ["date-and-time"]
 

benches/datetime_format.rs

@@ -1,12 +1,10 @@
 #![feature(test)]
-extern crate chrono;
-extern crate humantime;
 extern crate test;
 
 use std::io::Write;
 use std::time::{Duration, UNIX_EPOCH};
-use humantime::format_rfc3339;
 
+use humantime::format_rfc3339;
 
 #[bench]
 fn rfc3339_humantime_seconds(b: &mut test::Bencher) {

benches/datetime_parse.rs

@@ -1,12 +1,9 @@
 #![feature(test)]
-extern crate chrono;
-extern crate humantime;
 extern crate test;
 
 use chrono::{DateTime};
 use humantime::parse_rfc3339;
 
-
 #[bench]
 fn rfc3339_humantime_seconds(b: &mut test::Bencher) {
     b.iter(|| {

src/date.rs

@@ -364,12 +364,11 @@ impl fmt::Display for Rfc3339Timestamp {
 
 #[cfg(test)]
 mod test {
-    extern crate time;
-    extern crate rand;
-
     use std::str::from_utf8;
-    use self::rand::Rng;
     use std::time::{UNIX_EPOCH, SystemTime, Duration};
+
+    use rand::Rng;
+
     use super::{parse_rfc3339, parse_rfc3339_weak, format_rfc3339};
     use super::{format_rfc3339_millis, format_rfc3339_micros};
     use super::{format_rfc3339_nanos};

src/duration.rs

@@ -301,10 +301,10 @@ impl fmt::Display for FormattedDuration {
 
 #[cfg(test)]
 mod test {
-    extern crate rand;
-
     use std::time::Duration;
-    use self::rand::Rng;
+
+    use rand::Rng;
+
     use super::{parse_duration, format_duration};
     use super::Error;
 

src/wrapper.rs

@@ -3,8 +3,8 @@ use std::ops::Deref;
 use std::fmt;
 use std::time::{Duration as StdDuration, SystemTime};
 
-use duration::{self, parse_duration, format_duration};
-use date::{self, parse_rfc3339_weak, format_rfc3339};
+use crate::duration::{self, parse_duration, format_duration};
+use crate::date::{self, parse_rfc3339_weak, format_rfc3339};
 
 /// A wrapper for duration that has `FromStr` implementation
 ///