Issue 118 null literals

[timofriedlberlin]

This PR parses Null literals correctly and stated by the YAML spec: https://yaml.org/type/null.html

[coveralls]

Coverage increased (+0.2%) to 77.275% when pulling 003e8fc on timo-klarshift:issue-118-null-literals into 0b6739e on redhat-developer:master.

[JPinkney]

@itowlson Just wanted to cc you in on this because I think the kubernetes schema would need to be updated. In cases in the kubernetes schema where a value can be a null or string you'll have to update the type.

Currently, null is parsed as a string but that violates the yaml spec so its going to go back to parsing null as a NullAstNode and now null will match json schemas "type": "null"

[timofriedlberlin]

Just out of interest, when will this be released and upstreamed to vscode-yaml?

[JPinkney]

@timo-klarshift Probably in a couple of weeks