fix(fetch): timeout fetch if no response from the server

based on suggestion on JakeChampion/fetch#175

src/util/timeout.js

@@ -0,0 +1,8 @@
+export default function timeout(promise, ms = 30000) {
+  return new Promise(function (resolve, reject) {
+    setTimeout(function () {
+      reject(new Error('timeout'))
+    }, ms)
+    promise.then(resolve, reject)
+  })
+}