SwiftLint2

Deallocate memory after every linting

- Use `autoreleasepool(_:)`
- Call `File.invalidateCache()`

Instruments on linting Carthage 0.12,
maximum Persistent Bytes is reduced from 508.49MB to 170.74MB.
Total number of allocation does not increase. (If disposed memory was reused, it increases.)
Running Time of calling `File.invalidateCache()` is 381ms.
Running Time of calling `autoreleasepool(_:)` is 45ms.