fix(json-schema): add missing platforms property to cmds for

[dkarter]

Motivation

I've been getting errors from my editor that using platforms as a sibling of for under cmds is not supported, when it is in fact supported and respected by task

I believe this was missed on #980

Changes

• This change simply adds a small fix to the json schema to denote that
  platforms is allowed with for

Screenshots / Testing Instructions

🖼️ Before

🖼️ After

[vmaerten]

First of all, thanks for this!
Small comment, duplicate 3 times this key is not the way to go. Can you declare it under definitions then use it as a ref ?

like :

        "platforms": {
          "ref": "#/definitions/platforms"
        }

[dkarter]

@vmaerten great suggestion! Fixed in 4065c3e

[vmaerten]

Thanks