Faster build?

* https://eng.localytics.com/best-practices-and-common-mistakes-with-travis-ci/
* less than 10 min && cache << 1GB could be a first goal?

No file, test, or entry point is named. Start by reviewing the linked Travis CI guidance and locating the repository's build configuration, then measure the current build time and cache size; done means a specific, verified improvement toward the proposed limits.

索引モデルが issue の本文から書いたものです。