Modification of 1st parameter of $append

[HiroyasuNishiyama]

The following code produces { a: [ 1 ] } instead of { a: [] }.

var jsonata = require("jsonata");
var data = { a: [] };
var exp = jsonata("$append(a,[1])");
exp.evaluate(data);
console.log(data);

The 1st parameter of $append is modified as a side effect of $append call.
The documentation of $append do not mention this side effect.　Also, similar function for array such as $reverse or $sort do not modify their argument.

[andrew-coleman]

This is a bug. Many thanks for reporting.

[mattbaileyuk]

Fixed via #142