fix(lib/plugins): support node v0.12

lib/plugins.js

@@ -12,25 +12,27 @@
  * @return {Array} plugins PostCSS Plugins
  */
 module.exports = function plugins (config) {
-  let plugins = []
+  var plugins = []
 
   if (Array.isArray(config.plugins)) {
     plugins = config.plugins
 
-    plugins.forEach((plugin) => {
-      if (typeof plugin !== 'function') {
-        throw new TypeError(`
-          ${plugin} must be a function, did you require() it ?
-       `)
-      }
-    })
+    if (plugins.length > 0) {
+      plugins.forEach(function (plugin) {
+        if (typeof plugin !== 'function') {
+          throw new TypeError(
+            plugin + ' must be a function, did you require() it ?'
+          )
+        }
+      })
+    }
 
     return plugins
   } else {
     config = config.plugins
 
-    const load = (plugin, options) => {
-      if (options === null) {
+    var load = function (plugin, options) {
+      if (options === null || Object.keys(options).length === 0) {
         try {
           return require(plugin)
         } catch (err) {
@@ -46,8 +48,12 @@ module.exports = function plugins (config) {
     }
 
     Object.keys(config)
-      .filter((plugin) => config[plugin] !== false ? plugin : '')
-      .forEach((plugin) => plugins.push(load(plugin, config[plugin])))
+      .filter(function (plugin) {
+        return config[plugin] !== false ? plugin : ''
+      })
+      .forEach(function (plugin) {
+        return plugins.push(load(plugin, config[plugin]))
+      })
 
     return plugins
   }