fix: upgrade avsc from 5.4.20 to 5.4.21

Snyk has created this PR to upgrade avsc from 5.4.20 to 5.4.21.

See this package in NPM:
https://www.npmjs.com/package/avsc

See this project in Snyk:
https://app.snyk.io/org/codingtools/project/69f63852-fccf-4e2e-aeaf-6785477b4de5?utm_source=github&utm_medium=upgrade-pr

Author: snyk-bot

package.json

@@ -16,7 +16,7 @@
     "@oclif/plugin-commands": "^1.2.3",
     "@oclif/plugin-help": "^2.2.3",
     "@oclif/plugin-warn-if-update-available": "^1.7.0",
-    "avsc": "^5.4.20",
+    "avsc": "^5.4.21",
     "axios": "^0.19.2",
     "chalk": "^3.0.0",
     "codecov": "^3.6.5",