remove trailing whitespace

Author: Takashiidobe

library/alloc/src/collections/linked_list.rs

@@ -657,7 +657,7 @@ impl<T> LinkedList<T> {
 
     /// Provides a reference to the front element, or `None` if the list is
     /// empty.
-    /// 
+    ///
     /// This operation should compute in *O*(*1*) time.
     ///
     /// # Examples
@@ -679,7 +679,7 @@ impl<T> LinkedList<T> {
 
     /// Provides a mutable reference to the front element, or `None` if the list
     /// is empty.
-    /// 
+    ///
     /// This operation should compute in *O*(*1*) time.
     ///
     /// # Examples
@@ -707,7 +707,7 @@ impl<T> LinkedList<T> {
 
     /// Provides a reference to the back element, or `None` if the list is
     /// empty.
-    /// 
+    ///
     /// This operation should compute in *O*(*1*) time.
     ///
     /// # Examples
@@ -729,7 +729,7 @@ impl<T> LinkedList<T> {
 
     /// Provides a mutable reference to the back element, or `None` if the list
     /// is empty.
-    /// 
+    ///
     /// This operation should compute in *O*(*1*) time.
     ///
     /// # Examples