Feature: enable server-side-rendering (#17)

* Conditionally require picturefill to allow SSR

* Add can-use-dom

* fix: Add canUseDom guard on ieVersion check

Author: brettgullan

package.json

@@ -70,6 +70,7 @@
     "react-dom": "^15.0.1"
   },
   "dependencies": {
+    "can-use-dom": "^0.1.0",
     "glamorous": "^3.23.3",
     "picturefill": "^3.0.2",
     "prop-types": "^15.5.10"

src/components/Picture.jsx

@@ -1,17 +1,24 @@
 import React from "react";
 import PropTypes from "prop-types";
-import picturefill from "picturefill";
 import glamorous from "glamorous";
+import canUseDom from 'can-use-dom'
 
 const Img = glamorous.img();
 
 class Picture extends React.PureComponent {
     componentDidMount() {
-        picturefill();
+        // c.f. https://github.com/scottjehl/picturefill/pull/556
+        var picturefill;
+        try {
+            picturefill = require('picturefill');
+        } catch(x) {}
+        
+        if (picturefill) picturefill(); // browser
+        // else node
     }
 
     renderSources() {
-        const ieVersion = document.documentMode ? document.documentMode : -1;
+        const ieVersion = canUseDom && document.documentMode ? document.documentMode : -1;
         const { sources } = this.props;
 
         if (sources == null) {