Add global background color class to footer

(it's already on the header). Fixes #135

CHANGELOG.md

 The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/) and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
 
 
+## [2.35] - 2018-11-04 (@budparr)
+
+- Add global background color class to footer (it's already on the header). Fixes #135
+
 ## [2.34] - 2018-11-03 (@budparr)
 
 ### Added

layouts/partials/site-footer.html

-<footer class="bg-near-black bottom-0 w-100 pa3" role="contentinfo">
+<footer class="{{ .Site.Params.background_color_class | default "bg-black" }} bottom-0 w-100 pa3" role="contentinfo">
   <div class="flex justify-between">
   <a class="f4 fw4 hover-white no-underline white-70 dn dib-ns pv2 ph3" href="{{ .Site.BaseURL }}" >
     &copy; {{ now.Format "2006" }} {{ .Site.Title }}