Handle pseudo-browser environments when rendering server-side

Author: liseki

lib/utils/getPrefix.es6

@@ -1,5 +1,9 @@
 export default (function() {
-  if (typeof window === 'undefined') return '';
+  // Checking specifically for 'window.document' is for pseudo-browser server-side
+  // environments that define 'window' as the global context.
+  // E.g. React-rails (see https://github.com/reactjs/react-rails/pull/84)
+  if (typeof window === 'undefined' || typeof window.document === 'undefined') return '';
+
   // Thanks David Walsh
   let styles = window.getComputedStyle(document.documentElement, ''),
   pre = (Array.prototype.slice