CI: Appveyor has inconsistent cache hits

See: https://ci.appveyor.com/project/FormidableLabs/serverless-jetpack/builds/30391121#L5

```
Restoring build cache
Cache 'node_modules' - Restored
Cache 'test\packages\complex\npm\node_modules' - Restored
Cache 'test\packages\complex\yarn\node_modules' - Restored
Cache 'test\packages\dashboard\npm\node_modules' - Restored
Cache 'test\packages\dashboard\yarn\node_modules' - Restored
Cache 'test\packages\huge\npm\node_modules' - Restored
Cache 'test\packages\huge\yarn\node_modules' - Invalidated as some dependencies (test\packages\huge\yarn\yarn.lock) have changed
Cache 'test\packages\individually\npm\node_modules' - Restored
Cache 'test\packages\individually\yarn\node_modules' - Restored
Cache 'test\packages\monorepo\npm\node_modules' - Restored
Cache 'test\packages\monorepo\yarn\node_modules' - Restored
Cache 'test\packages\simple\npm\node_modules' - Restored
Cache 'test\packages\simple\yarn\node_modules' - Restored
Cache 'test\packages\webpack\npm\node_modules' - Restored
Cache 'test\packages\webpack\yarn\node_modules' - Invalidated as some dependencies (test\packages\webpack\yarn\yarn.lock) have changed
Cache 'test\packages\complex\npm\layers\with-deps\nodejs\node_modules' - Restored
Cache 'test\packages\monorepo\npm\functions\another\node_modules' - Restored
Cache 'test\packages\monorepo\npm\functions\base\node_modules' - Restored
Cache 'test\packages\monorepo\npm\lib\camel\node_modules' - Restored
Cache 'test\packages\complex\yarn\layers\with-deps\nodejs\node_modules' - Restored
Cache 'test\packages\monorepo\yarn\functions\base\node_modules' - Restored
Cache 'C:\Users\appveyor\AppData\Local\Yarn' - Restored
Cache 'C:\Users\appveyor\AppData\Roaming\npm-cache' - Restored
```