Support Neon 0.5

[jhg]

    Updating crates.io index
error: failed to select a version for `neon-sys`.
    ... required by package `neon-runtime v0.5.0`
    ... which is depended on by `neon v0.5.0`
    ... which is depended on by `flare_node v0.1.0 (~/Repositories/draco/flare_node/native)`
versions that meet the requirements `=0.5.0` are: 0.5.0

the package `neon-sys` links to the native library `neon`, but it conflicts with a previous package which links to `neon` as well:
package `neon-sys v0.4.0`
    ... which is depended on by `neon-build v0.4.0`
    ... which is depended on by `neon v0.4.0`
    ... which is depended on by `neon-serde v0.4.0`
    ... which is depended on by `flare_node v0.1.0 (~/Repositories/draco/flare_node/native)`

failed to select a version for `neon-sys` which could resolve this conflict

Software using neon-serde can not update neon, maybe because breaking changes in neon-runtime and then they update to 0.5 (and versions 0.4.1 and 0.4.2 were "yanked"): https://github.com/neon-bindings/neon/releases/tag/0.5.0