Cmdliner deprecation error when building

[manuca]

I tried building Opium from the current master branch and got a deprecation error from the cmdliner package which broke the build apparently.

I realized by looking into the upstream sources that cmdliner got that deprecation error fairly recently.

I hacked around the issue by adding a version specifier in the dune-project file at the root of Opium.

-cmdliner
+(cmdliner (<= 1.0.4))

I did manage to build the project after the change.

Just wanted to let you know about the issue but I don't know if that's the correct way to fix it.