curl version change to work around bug

[baentsch]

Fixes #236

[baentsch]

Prodding @dstebila @bhess for review & approval: After the oqs-provider release this PR can close the one known defect on oqs-demos prior to tagging it and its docker images "0.9.0" and considering the release round complete.

[baentsch]

Oops -- one more thought: Didn't we want to update/release openssh, too, before tagging oqs-demos? @praveksharma ? But then again, that project seems dead: No activity for about 6 months; also I didn't find an option to tell (algorithm) versions apart in different builds, so why bother? Or is there a way to see, e.g., which McEliece/liboqs version is used in a specific oqs-openssh version? If not, there really may be no reason to release oqs-openssh: The most current version will simply run with liboqs 0.9.0 code and accordingly not interoperate with 0.8.0 builds -- but that doesn't seem to be a concern anyway, right @dstebila ?

[baentsch]

Update to the above: When open-quantum-safe/openssh#148 gets merged (not by me but someone knowledgeable in OpenSSH), tagging a release would be a minor thing: Would you want to do that too, @praveksharma ? After that, merging this PR is really the last thing: When done, all resultant automatically generated docker images should be tagged 0.9.0 and we can consider the 0.9.0 release cycle complete.