Doc: Update node version in BUILD.md (#5616)

* Update node version in BUILD.md

Apparently node 16.0.0 may not work, see https://github.com/laurent22/joplin/issues/5608

* Update BUILD.md

* Change node 16.11 -> node 14

BUILD.md

@@ -18,7 +18,7 @@ There are also a few forks of existing packages under the "fork-*" name.
 
 ## Required dependencies
 
-- Install node 10+ - https://nodejs.org/en/
+- Install node 14+ - https://nodejs.org/en/
 - macOS: Install Cocoapods - `brew install cocoapods`
 - Windows: Install Windows Build Tools - `npm install -g windows-build-tools --vs2015`
 - Linux: Install dependencies - `sudo apt install libnss3 libsecret-1-dev python rsync`