Update dependencies

[taiki-e]

• either 1.4 -> 1.5
• num_cpus 1.8.0 -> 1.9
• lazy_static 1.1.0 -> 1.2
• syn 0.15.22 -> 0.15.25

This PR mainly updates minor versions of dependencies.
num_cpus and lazy_static seem to be stable enough, so I think that it is probably OK without specifying a patch version.
Also, non_camel_case_type warning was allowed in dtolnay/syn#563, so I would like to include updating syn.

[taiki-e]

Update of rand was split into #1425.

[cramertj]

What's the point of bumping the minimum required version of these dependencies? AFAICT all this would do is force end-users to update, without actually providing any new functionality here (since users would already get the newer versions by default in a cargo build w/o a lockfile or a cargo update).

[taiki-e]

(since users would already get the newer versions by default in a cargo build w/o a lockfile or a cargo update)

I wrote this PR because I found older versions in dependencies when I built it locally, but I seem to have forgotten this.