chore: update nvmrc from node8 to node14

Couldn't run lerna publish due to the following error
yargs parser supports a minimum Node.js version of 10. Read our version support policy: https://github.com/yargs/yargs-parser#supported-nodejs-versions

Given that AWS Lambda runtime now supports v14,
we are updating nvmrc to node14

.nvmrc

@@ -1 +1 @@
-8.10.0
+14.16.1