Modify artifact numbering in feature table filtering tutorial

[lina-kim]

The tutorial contains an extraneous filtering step after filtering for autoFMT study samples:

This step was removed in the video tutorial. Consequently, downstream artifact names are now off by 1, e.g. filtered-table-1.qza in the video corresponds to filtered-table-2.qza in the written tutorial. All references to these file names should be updated in the written tutorial.

[gregcaporaso]

Thanks @lina-kim! I'm making this change now.

[gregcaporaso]

Addressed in #38.