Make Wu-Wei Compatible with Older versions of Node

[wukefe]

Failed to run the tool with node v4.3.2 on MacOS, however, it worked when node was upgraded to v7.5.0. Another test on Ubuntu found node v6.9.5 worked as well.

Error message

... wu-wei-sable/lib/config.js:160
      let err = validate.errors[0]
      ~~~

SyntaxError: Block-scoped declarations (let, const, function, class) not yet
supported outside strict mode

[elavoie]

This is a known issue, I have used newer language constructs from the latest version of JavaScript that require a recent node engine. The package.json file specifies:

"engines" : { "node" : "^6.3.1" }

The minimum version required.

[elavoie]

I am actually reopening the issue and renaming it.

[elavoie]

One approach that should not be too hard to use would be to compile all the sources with Babel.