interval: Update for 2nd edition.

interval/Cargo.toml

@@ -2,5 +2,6 @@
 name = "interval"
 version = "0.1.0"
 authors = ["You <you@example.com>"]
+edition = "2018"
 
 [dependencies]

interval/src/lib.rs

@@ -1,17 +1,25 @@
+#![warn(rust_2018_idioms)]
+#![allow(elided_lifetimes_in_paths)]
+
 #[derive(Debug, PartialEq)]
 struct Interval<T> {
     lower: T, // inclusive
-    upper: T  // exclusive
+    upper: T, // exclusive
 }
 
 use std::cmp::{Ordering, PartialOrd};
 
 impl<T: PartialOrd> PartialOrd<Interval<T>> for Interval<T> {
     fn partial_cmp(&self, other: &Interval<T>) -> Option<Ordering> {
-        if self == other { Some(Ordering::Equal) }
-        else if self.lower >= other.upper { Some(Ordering::Greater) }
-        else if self.upper <= other.lower { Some(Ordering::Less) }
-        else { None }
+        if self == other {
+            Some(Ordering::Equal)
+        } else if self.lower >= other.upper {
+            Some(Ordering::Greater)
+        } else if self.upper <= other.lower {
+            Some(Ordering::Less)
+        } else {
+            None
+        }
     }
 }