Revert "Cache the hosted directory under .pub-cache instead of all of .pub-cache." (#11507)

This reverts commit 0cfd3dec239faf3c13ce759df15ddab226545e8c.

.travis.yml

@@ -28,4 +28,4 @@ script:
   - (./bin/cache/dart-sdk/bin/dart ./dev/bots/test.dart && ./dev/bots/travis_upload.sh)
 cache:
   directories:
-    - $HOME/.pub-cache/hosted
+    - $HOME/.pub-cache
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