Rollup merge of rust-lang#41019 - mandeep:fix-vec-swapremove-docs, r=BurntSushi

Fixed typo in doc comments for swap_remove

While reading the Vec docs, I came across the docs for swap_remove. I believe there is a typo in the comment and ```return``` should be ```returns```. This PR fixes this issue.

I also feel that the entire doc comment is a bit of a run-on and could be changed to something along the lines of ```Removes an element from anywhere in the vector and returns it. The vector is mutated and the removed element is replaced by the last element of the vector. ```

Thoughts?

Author: frewsxcv

src/libcollections/vec.rs

@@ -678,8 +678,9 @@ impl<T> Vec<T> {
         self.len = len;
     }
 
-    /// Removes an element from anywhere in the vector and return it, replacing
-    /// it with the last element.
+    /// Removes an element from the vector and returns it.
+    ///
+    /// The removed element is replaced by the last element of the vector.
     ///
     /// This does not preserve ordering, but is O(1).
     ///