fixes #203

[affeldt-aist]

fixes #203

fyi: @t6s

[t6s]

what is this remaining ci error?

[affeldt-aist]

I am not sure, it looks like a dependency problem related to interval:

 error: Cannot build '/nix/store/3yg585szzz7w56hsdnpcwjzsrc9y59mw-coq9.1-interval-4.11.3.drv'.
       Reason: 1 dependency failed.
       Output paths:
         /nix/store/bsmvwsyppcfyasn00l4mndmdxdlnl0iv-coq9.1-interval-4.11.3
error: Build failed due to failed dependency

[t6s]

sh: -o: not found

some shell variable became empty due to dependency changes, and -o appeared at a wrong place?