Run cargo update on dependencies

[alexcrichton]

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