Rename backgroundColors to backgroundColor

defaultConfig.stub.js

@@ -8,7 +8,7 @@ module.exports = {
   variants: {
     appearance: ['responsive'],
     backgroundAttachment: ['responsive'],
-    backgroundColors: ['responsive', 'hover', 'focus'],
+    backgroundColor: ['responsive', 'hover', 'focus'],
     backgroundPosition: ['responsive'],
     backgroundRepeat: ['responsive'],
     backgroundSize: ['responsive'],

defaultTheme.js

@@ -154,7 +154,7 @@ module.exports = function() {
       wide: '0.05em',
     },
     textColors: theme => theme.colors,
-    backgroundColors: theme => theme.colors,
+    backgroundColor: theme => theme.colors,
     backgroundPosition: {
       bottom: 'bottom',
       center: 'center',

plugins/backgroundColor.js

@@ -0,0 +1 @@
+module.exports = require('../lib/plugins/backgroundColor').default

plugins/backgroundColors.js

@@ -1 +0,0 @@
-module.exports = require('../lib/plugins/backgroundColors').default

src/corePlugins.js

@@ -2,7 +2,7 @@ import preflight from './plugins/preflight'
 import lists from './plugins/lists'
 import appearance from './plugins/appearance'
 import backgroundAttachment from './plugins/backgroundAttachment'
-import backgroundColors from './plugins/backgroundColors'
+import backgroundColor from './plugins/backgroundColor'
 import backgroundPosition from './plugins/backgroundPosition'
 import backgroundRepeat from './plugins/backgroundRepeat'
 import backgroundSize from './plugins/backgroundSize'
@@ -73,7 +73,7 @@ export default function(config) {
     lists,
     appearance,
     backgroundAttachment,
-    backgroundColors,
+    backgroundColor,
     backgroundPosition,
     backgroundRepeat,
     backgroundSize,