Build Cache for Gradle v2.20.19

Changelog
1

What’s Changed

  • Bump bitrise-build-cache CLI to v2.8.15 — SSW-3019: adds an instrumentation-fingerprint probe to the gradle-mirrors init script (reports jacoco/mockk/byte-buddy/stub-DisplayMetrics per Robolectric test task) + per-jar noncompatWidthPixels:present|MISSING in the classpath probe. Opt-out; never fails a build.