Bump axios from 0.19.2 to 0.21.1 in /demo

Bumps [axios](https://github.com/axios/axios) from 0.19.2 to 0.21.1.
- [Release notes](https://github.com/axios/axios/releases)
- [Changelog](https://github.com/axios/axios/blob/v0.21.1/CHANGELOG.md)
- [Commits](axios/axios@v0.19.2...v0.21.1)

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

demo/package-lock.json

@@ -42,7 +42,7 @@
     "agora-rtc-sdk-ng": "^4.2.1",
     "ansi-styles": "^3.2.0",
     "autoprefixer": "7.1.1",
-    "axios": "^0.19.0",
+    "axios": "^0.21.1",
     "babel-core": "6.25.0",
     "babel-eslint": "10.1.0",
     "babel-jest": "^24.9.0",