add changes from v0.3

pages/_error.js

@@ -0,0 +1,39 @@
+import React from 'react'
+
+export default class Error extends React.Component {
+  static getInitialProps({ res, err }) {
+    let statusCode = null
+    if (res) statusCode = res.statusCode
+    else if (err) statusCode = err.statusCode
+    return { statusCode }
+  }
+
+  render() {
+    const { statusCode } = this.props
+
+    return (
+      <div className="fill">
+        <h4>
+          {(() => {
+            if (statusCode === 404) {
+              return (
+                <>
+                  <span>404</span> | This page could not be found
+                </>
+              )
+            }
+            return statusCode ? `Error: ${statusCode}` : 'An error occurred...'
+          })()}
+        </h4>
+
+        <style jsx>{`
+          div {
+            display: flex;
+            align-items: center;
+            justify-content: center;
+          }
+        `}</style>
+      </div>
+    )
+  }
+}