On Travis CI, a pull request build reuses the target branch cache; it does not build up its own. If your PR build seems to ignore recent dependency changes, check what the base branch cache contains.

Context: From the official Travis CI caching docs. Cache lookup for pull request builds falls back to the target branch cache, not a cache of their own, and branch caches are keyed per branch. The docs also describe which directories are cached by default per language and that caches are stored per branch. Expecting a PR build to warm its own cache from scratch misunderstands the lookup order.