ensure single package for ui-keyring (#120)

package.json

@@ -2,7 +2,7 @@
   "version": "0.38.0-beta.5",
   "private": true,
   "engines": {
-    "node": "^10.13.0",
+    "node": ">=10.13.0",
     "yarn": "^1.10.1"
   },
   "homepage": ".",

packages/ui-keyring/src/index.ts

@@ -2,8 +2,12 @@
 // This software may be modified and distributed under the terms
 // of the Apache-2.0 license. See the LICENSE file for details.
 
+import { assertSingletonPackage } from '@polkadot/util';
+
 import keyring, { Keyring } from './Keyring';
 
+assertSingletonPackage('@polkadot/ui-keyring');
+
 export default keyring;
 
 export {