Ensure chunk size is not too small (V141)

[JavierDiezSierra]

[JavierDiezSierra]

It would be recommended that the chunksize of the time and time_bnds variables has equal to time dimension.

Small chunk size of the time dimensios are not recommende since it slows down the access to the information (https://github.com/PCMDI/cmor/issues/601)

[JavierDiezSierra]

Linked pull request: #13