doc: fix heading level for div et al builtins
Heading level should match that of 'len', 'close', 'and', and 'or'.
Signed-off-by: Paul Jolly <paul@myitcv.io>
Change-Id: I77514d4b0114b17a2bbba60ded5f4b0df2c3f974
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/528104
Unity-Result: CUEcueckoo <cueckoo@cuelang.org>
TryBot-Result: CUEcueckoo <cueckoo@cuelang.org>
Reviewed-by: Marcel van Lohuizen <mpvl@gmail.com>