get error when installing:  rollbackFailedOptional:

Sorry, I know it may not be related to your code, but hope its worth mentioning. I could not find an answer elsewhere.

```
root@OpenHAB:~# node -v
v10.19.0
root@OpenHAB:~# npm -v
6.14.4
root@OpenHAB:~# npm i frontail -g
[..................] / rollbackFailedOptional: verb npm-session 3be19b4bf6ded776
[..................] / rollbackFailedOptional: verb npm-session 3be19b4bf6ded776
```