Astropy votable framework gives several warnings when loading filter data from cache

[jaladh-singhal]

When loading filter data from cache by using functions like load_filter_index(), loads of warnings W06: Invalid UCD ‘x’: explanation occurs.

The cause is already identified: When filter data is downloaded as cache using download_filter_data(), W42: No XML namespace specified occurs, indicating that astropy votable framework is unable to identify version of SVO votable format (i.e. v1.1) - strange?! Thus when cache_as_votable() saves the table in cache as votable, the default v1.2 gets used by astropy. Thus ucd checking occurs while parsing it and hence several W06 occurs when loading the data.

It needs to be identified that what makes astropy votable framework unable to identify version of SVO votable format. And then take necessary steps to resolve it.