Upgrade dependency ranges

[csala]

The latest versions of the libraries pandas, sktime and pomegranate are not supported by sdmetrics:

Library	Upper bound (unsupported)	Latest release
pandas	1.1.5	1.3.1
pomegranate	0.14.2	0.14.5
sktime	0.6	0.7.0

We should investigate why and update the code if necessary to support them.

[fealho]

The maximum requirement for pandas comes from Copulas, so I think that should be discussed here.

The issue with pomegranate is that there are no wheels for py36 after 0.14.1.

sktime runs into a cannot import name 'TimeSeriesForestClassifier' which I'm currently investigating.

[katxiao]

sdv-dev/Copulas#266 addresses pandas, and #81 addresses sktime. Since pomegranate is now marked as optional, I am going to close this issue. We can open another issue if we want to bump the optional pomegranate range after we stop supporting py36.