* stop roll() from failing if the new cache has no files
Today I stumbled upon an error where it would fail when the cache folder was not present
```(typescript) Error: ENOENT: no such file or directory, rename 'REDACTED\node_modules\.cache\rollup-plugin-typescript2/rpt2_759e2fd8d3f20c1a0805faf5404af6bea36632fd/code/cache_' -> 'REDACTED\node_modules\.cache\rollup-plugin-typescript2/rpt2_759e2fd8d3f20c1a0805faf5404af6bea36632fd/code/cache'```
This PR fixes it by checking its existence before trying to rename it
* use existsSync instead of fs.existsSync
* use renameSync instead of fs.renameSync
