Short Answer questions should not have a format to their answers

[fuhrmanator]

See ets-cfuhrman-pfe/EvalueTonSavoir#176 for the use case.

In the test at:

GIFT-grammar-PEG.js/tests/questions/shortAnswer1.json

Lines 15 to 20 in 84236c6

	{
	"isCorrect": true,
	"weight": null,
	"text": {"format":"moodle", "text":"nobody"},
	"feedback": null
	}

it's clear that the parser expects a format for short answers, which is not compatible with Moodle:

At

GIFT-grammar-PEG.js/GIFT.pegjs

Line 212 in 84236c6

= answer:RichText _

RichText should probably be PlainText.