kellpossible
Update Fluent syntax crate
This PR is mostly to check that the upstream releases I just did of the project Fluent crates isn't causing trouble for major downstream consumers. The fluent-syntax release is technically a breaking one (we're still stick in zero-version land), but the breakage is just fixing an issue with a dependency mistakenly being conflated with a feature name. It shouldn't affect this project directly.
The new feature allowing serializing and deserializing the AST during parsing might be useful to this project, but that's up to you folks. Also in the next release we should have source position spans in the parser which might be useful for error messages or whatever...it didn't quite land in 0.12.0 but it should be along eventually.
