Fix lints

Author: udoprog

src/map/storage/boolean.rs

@@ -3,7 +3,6 @@
 #![allow(missing_copy_implementations)]
 
 use core::iter;
-use core::mem;
 use core::option;
 
 use crate::map::{Entry, MapStorage, OccupiedEntry, VacantEntry};
@@ -244,9 +243,9 @@ impl<V> MapStorage<bool, V> for BooleanMapStorage<V> {
     #[inline]
     fn insert(&mut self, key: bool, value: V) -> Option<V> {
         if key {
-            mem::replace(&mut self.t, Some(value))
+            self.t.replace(value)
         } else {
-            mem::replace(&mut self.f, Some(value))
+            self.f.replace(value)
         }
     }
 

src/map/storage/option.rs

@@ -1,5 +1,4 @@
 use core::iter;
-use core::mem;
 use core::option;
 
 use crate::map::{Entry, MapStorage, OccupiedEntry, VacantEntry};
@@ -274,7 +273,7 @@ where
     fn insert(&mut self, key: Option<K>, value: V) -> Option<V> {
         match key {
             Some(key) => self.some.insert(key, value),
-            None => mem::replace(&mut self.none, Some(value)),
+            None => self.none.replace(value),
         }
     }
 

src/map/storage/singleton.rs

@@ -1,5 +1,3 @@
-use core::mem;
-
 use crate::map::{Entry, MapStorage};
 use crate::option_bucket::{NoneBucket, OptionBucket, SomeBucket};
 
@@ -75,7 +73,7 @@ where
 
     #[inline]
     fn insert(&mut self, _: K, value: V) -> Option<V> {
-        mem::replace(&mut self.inner, Some(value))
+        self.inner.replace(value)
     }
 
     #[inline]