Update export tutorial to match new q2cli API

[thermokarst]

The changes introduced in qiime2/q2cli#189 are currently breaking the build process for the docs, due to API changes:

Running command: qiime tools export feature-table.qza --output-dir exported-feature-table

Extension error:
	
Command 'qiime tools export feature-table.qza --output-dir exported-feature-table' exited with non-zero return code 2.

stdout:
	
stderr:
Error: no such option: --output-dir

https://busywork.qiime2.org/teams/main/pipelines/master-distribution/jobs/integration/builds/120

The command (or commands) need to be updated to match the changes introduced in qiime2/q2cli#189.

Please note, this will require searching for all references to qiime tools export in the current docs source to ensure that any other command references are handled, besides just the one mentioned in the error above.

[thermokarst]

The changes proposed in qiime2/q2cli#191 & qiime2/q2cli#194 will need to be handled, too.