Rollup merge of #74218 - GuillaumeGomez:search-results-bottom-margin, r=Dylan-DPC

Rollup merge of #74218 - GuillaumeGomez:search-results-bottom-margin, r=Dylan-DPC

Add margin after doc search results

I found it not really on computer that the last result is right at the bottom of the page. I find it better with margin below (especially when you hover the last element!). A screenshot to show the result:

![Screenshot from 2020-07-10 16-32-23](https://user-images.githubusercontent.com/3050060/87166097-6103a580-c2cb-11ea-81a8-12772cf20f64.png)

r? @kinnison
cc @rust-lang/rustdoc @Manishearth @jyn514