Fix jquery-ui autocomplete styles

The autocomplete functionality was working but the list items were appearing on
a transparent background.

It looks like I introduced this problem in
419249e when I changed from using `require` to
`@import` to load the autocomplete styles. I need to use `require` because
'jquery-ui/autocomplete' has additional `require` statements that all need to
be processed by Sprockets.

It looks like I may have been able to use the jquery-ui-sass-rails[1] Gem to
avoid having to revert to Sprockets, but I think my approach is a little
simpler.

[1]: https://github.com/jhilden/jquery-ui-sass-rails

app/assets/stylesheets/application.scss

@@ -1,4 +1,7 @@
-@import "jquery-ui/autocomplete";
+/*
+ *= require jquery-ui/autocomplete
+ */
+
 @import "bootstrap-sprockets";
 @import "bootstrap";