fix documentation generation

[baentsch]

Fixes #1711.

• Does this PR change the input/output behaviour of a cryptographic algorithm (i.e., does it change known answer test values)? (If so, a version bump will be required from x.y.z to x.(y+1).0.)
• Does this PR change the list of algorithms available -- either adding, removing, or renaming? Does this PR otherwise change an API? (If so, PRs in fully supported downstream projects dependent on these, i.e., oqs-provider and OQS-OpenSSH will also need to be ready for review and merge by the time this is merged.)

[baentsch]

This PR does not impact the Travis files, so I'm assuming that stuff if broken asking for someone more knowledgeable regarding those platforms to take a look (@bhess?).

[baentsch]

asking for someone more knowledgeable

disregard. Travis passes after requesting a re-run.

[bhess]

This PR does not impact the Travis files, so I'm assuming that stuff if broken asking for someone more knowledgeable regarding those platforms to take a look (@bhess?).

Seems there was a glitch with Travis, I've re-run it and it works now.

[bhess]

Looks like Travis errored again after the merge, I've created a ticket with them about the issue.