travis: use v1-install instead of --lib
travis: use v1-install instead of --lib

The --lib feature is experimental and not properly defined yet as of
2021-04-09:

https://github.com/haskell/cabal/issues/6481
https://github.com/haskell/cabal/commit/b0e88b1c0bb6d745f9ff7a728c6dcada748a68ea#diff-d6d1b75715cf9178b2e648b3eb550389eb83c8b64cd832d391ea05b2f3ed773b

When cabal developers figure it out, I'll switch to use v2-install.
Until then, I'll keep using v1 whereever possible.

rudymatela/speculate