`spec-tools.data-spec/spec` has a wrong assert

[Eugene Pakhomov]

Its 1-arity signature, followed by the assert:

[{data :spec name :name nested? ::nested? :as opts}]
(assert spec "missing :spec predicate in data-spec")

Notice how it asserts spec instead of data. I got confused by it more than once myself while reading sources, seeing spec in one place and data in another.