Outdated warning when using default filter

[kaylynb]

When using a default filter without specifying boolean, nunjucks displays an outdated deprecation warning.

Ex:

{{ x | default('y') }}

produces the following warning:

[nunjucks] Warning: the "default" filter was used without specifying the type of comparison. 2.0 changed the default behavior from boolean (val ? val : def) to strictly undefined, so you should make sure that doesn't break anything. Be explicit about this to make this warning go away, or wait until 2.1. See http://mozilla.github.io/nunjucks/templating.html#defaultvalue-default-boolean

The warning says 'or wait until 2.1.', and the documentation says it will be removed in the next version.

Appears to still be in master as of today:

nunjucks/src/filters.js

Lines 70 to 77 in 90e3913

	console.log(
	'[nunjucks] Warning: the "default" filter was used without ' +
	'specifying the type of comparison. 2.0 changed the default ' +
	'behavior from boolean (val ? val : def) to strictly undefined, ' +
	'so you should make sure that doesn\'t break anything. ' +
	'Be explicit about this to make this warning go away, or wait until 2.1. ' +
	'See http://mozilla.github.io/nunjucks/templating.html#defaultvalue-default-boolean'
	);

Does this need a PR to update documentation and/or remove the warning?

[carljm]

Closed with merge of #567.