Github user r-kamath commented on the issue:
https://github.com/apache/zeppelin/pull/2923
@VipinRathor can you try removing `npm cache clear` from .travis.yml ?
otherwise add `--force`.
npm doc says.
> All data that passes through the cache is fully verified for integrity on
both insertion and extraction. Cache corruption will either trigger an error,
or signal to pacote that the data must be refetched, which it will do
automatically. For this reason, it should never be necessary to clear the cache
for any reason other than reclaiming disk space, thus why clean now requires
--force to run.
[details](https://docs.npmjs.com/cli/cache#details)
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