pkg/crypto/hmac: fix package documentation
pkg/crypto/hmac: fix package documentation

Change-Id: I655aa7a95e36ffea34f5409d533bb070565317f5
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/9683
Reviewed-by: CUE cueckoo <0f32a827c9a5f00281f936ac78b5ef3ba80a954c@gmail.com>
Reviewed-by: Paul Jolly <a027184a55211cd23e3f3094f1fdc728df5e0500@myitcv.org.uk>

cuelang/cue