Use "Fira Sans" for crate list font

Fira Sans is what's used for module lists and other item lists.
Previously, the default body font, "Source Serif Pro", was used for
crate lists, which didn't visually match other item lists.

src/librustdoc/html/render/mod.rs

@@ -1062,12 +1062,13 @@ themePicker.onblur = handleThemeButtonsBlur;
             let content = format!(
                 "<h1 class='fqn'>\
                      <span class='in-band'>List of all crates</span>\
-                </h1><ul class='mod'>{}</ul>",
+                </h1>\
+                <ul class='crate mod'>{}</ul>",
                 krates
                     .iter()
                     .map(|s| {
                         format!(
-                            "<li><a class=\"mod\" href=\"{}index.html\">{}</a></li>",
+                            "<li><a class=\"crate mod\" href=\"{}index.html\">{}</a></li>",
                             ensure_trailing_slash(s),
                             s
                         )