Run cargo update on dependencies (#868)

Looks like we're able to actually drop a good number of various deps,
especially some large-ish ones like syn 0.14!

      Adding proc-macro2 v1.0.8
      Adding syn v1.0.14

    Removing base64 v0.10.1
    Removing cloudabi v0.0.3
    Removing crossbeam-utils v0.6.6
    Removing failure v0.1.6
    Removing failure_derive v0.1.6
    Removing fuchsia-cprng v0.1.1
    Removing proc-macro2 v0.4.30
    Removing proc-macro2 v1.0.7
    Removing quote v0.6.13
    Removing rand_core v0.3.1
    Removing rand_core v0.4.2
    Removing rand_os v0.1.3
    Removing rdrand v0.4.0
    Removing syn v0.14.9
    Removing syn v1.0.13
    Removing synstructure v0.9.0
    Removing unicode-xid v0.1.0
    Removing wincolor v1.0.2

    Updating arbitrary v0.3.2 -> v0.3.3
    Updating arrayref v0.3.5 -> v0.3.6
    Updating constant_time_eq v0.1.4 -> v0.1.5
    Updating crates.io index
    Updating derive_arbitrary v0.3.1 -> v0.3.3
    Updating indexmap v1.3.0 -> v1.3.1
    Updating itoa v0.4.4 -> v0.4.5
    Updating jobserver v0.1.18 -> v0.1.19
    Updating memchr v2.2.1 -> v2.3.0
    Updating num_cpus v1.11.1 -> v1.12.0
    Updating proc-macro-error v0.4.4 -> v0.4.5
    Updating proc-macro-error-attr v0.4.3 -> v0.4.5
    Updating quickcheck v0.9.0 -> v0.9.2
    Updating rand v0.7.2 -> v0.7.3
    Updating redox_users v0.3.1 -> v0.3.4
    Updating rust-argon2 v0.5.1 -> v0.7.0
    Updating rustversion v1.0.1 -> v1.0.2
    Updating serde_json v1.0.44 -> v1.0.45
    Updating structopt v0.3.7 -> v0.3.8
    Updating structopt-derive v0.4.0 -> v0.4.1
    Updating termcolor v1.0.5 -> v1.1.0
    Updating thread_local v1.0.0 -> v1.0.1
    Updating toml v0.5.5 -> v0.5.6
    Updating winapi-util v0.1.2 -> v0.1.3