Revert "get rid of polyfill since this is just chrome anyway."

This reverts commit a935a8c026.

extension/popup.jsx

@@ -1,3 +1,4 @@
+import browser from 'webextension-polyfill'
 import {render} from 'react-dom'
 import {getPublicKey} from 'nostr-tools'
 import {bech32} from 'bech32'
@@ -8,7 +9,7 @@ function Popup() {
   let keys = useRef([])
 
   useEffect(() => {
-    chrome.storage.local.get('private_key').then(results => {
+    browser.storage.local.get('private_key').then(results => {
       if (results.private_key) {
         let hexKey = getPublicKey(results.private_key)
         let npubKey = bech32.encode(