Spec incorrectly disallows use of <label/> before <name/>

[rmzelle]

Compare https://github.com/citation-style-language/schema/blob/v1.0.1/csl.rnc#L423:

  rendering-element.names =
    element cs:names {
      names.attributes,
      ((names.name?, names.et-al?) & names.label*),
      names.substitute?
}

with http://docs.citationstyles.org/en/stable/specification.html#label-in-cs-names:

The optional cs:label element (see label) must be included after the cs:name and cs:et-al elements, but before the cs:substitute element.

(mismatch first identified in https://github.com/citation-style-language/styles/pull/2389#discussion_r94197372)