Bump subprocess from 0.2.13 to 0.2.15

Bumps [subprocess](https://github.com/hniksic/rust-subprocess) from 0.2.13 to 0.2.15.
- [Commits](hniksic/rust-subprocess@release/0.2.13...release/0.2.15)

---
updated-dependencies:
- dependency-name: subprocess
  dependency-version: 0.2.15
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

Cargo.lock

@@ -52,5 +52,5 @@ expectorate = "1.0"
 slog-async = "2.8"
 slog-term = "2.9"
 structopt = "0.3"
-subprocess = "0.2.13"
+subprocess = "0.2.15"
 proptest = "1.9.0"