Update from Node 14.5.0 to Node 16.20.0 (#521)

Author: timostamm

Diff for: .nvmrc

@@ -0,0 +1 @@
+v16.20.0

Diff for: CONTRIBUTING.md

@@ -15,7 +15,7 @@ Just [start a discussion](https://github.com/timostamm/protobuf-ts/discussions/n
 
 ### Building this project 
 
-Building and testing this project requires `node` (14.5.0), `npm`, `protoc` (3.12.3), 
+Building and testing this project requires `node`, `npm`, `protoc`, 
 `make`, `git`, and `go`.  
 
 - `go` is required for the Twirp transport client compatibility test suite

Diff for: MANUAL.md

@@ -1430,7 +1430,7 @@ size comparison.
 
 ## Running in Node.js
 
-`protobuf-ts` is tested with Node.js version 14.5.0. 
+`protobuf-ts` is tested with Node.js version 16.20.0. 
 
 Older versions certainly work, but may not support all features or require polyfills. 
 For example, if you target lower than ES2020 to run in an older node version, you