ibus-engines.typing-booster: support french by default

This has been postponed[1] because of an unclear state of the french
dictionary provided by hunspell[2].

[1] https://github.com/NixOS/nixpkgs/pull/46779#issuecomment-422764601
[2] https://github.com/NixOS/nixpkgs/issues/46940#issuecomment-423288963