Use Node.js 14 tsconfig configuration

[n1ru4l]

See https://github.com/nodejs/release#release-schedule

The minimum version supported in maintenance mode is Node.js 14, thus it is legit to increase the target ECMA version.

e.g. to https://github.com/tsconfig/bases/blob/main/bases/node14.json

LTS graphic: https://github.com/nodejs/release#release-schedule

Current version: https://github.com/supertokens/supertokens-node/blob/76a983fae157a8d4781f0eb9dac017cffac587e0/lib/tsconfig.json#L3

This change will result in less verbose transforms (such as async await to generators etc.)