Bump peer dependency for React

Based on #293,
it appears this package works fine with React 18

Author: fongandrew

package.json

@@ -54,7 +54,7 @@
   ],
   "peerDependencies": {
     "codemirror": "5.x",
-    "react": ">=15.5 <=17.x"
+    "react": ">=15.5 <=18.x"
   },
   "devDependencies": {
     "@babel/preset-env": "7.10.1",