Bump bob-builder from 0.0.18 to 0.0.19 (#1088)

Bumps [bob-builder](https://github.com/heroku-python/bob-builder) from 0.0.18 to 0.0.19.
- [Release notes](https://github.com/heroku-python/bob-builder/releases)
- [Commits](https://github.com/heroku-python/bob-builder/commits)

Signed-off-by: dependabot[bot] <[email protected]>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

requirements.txt

@@ -1,5 +1,5 @@
 # Dependencies for generating/publishing Python binaries.
-bob-builder==0.0.18
+bob-builder==0.0.19
 
 # Sub-dependencies of bob-builder.
 boto==2.49.0