Should install zip

[taoyouh]

The new "export user data" function in 4.9.6 requires zip function to work, but the default installation doesn't include zip.
I think we should install zip in the image.

[tianon]

I've managed to reproduce with a stock WordPress setup:

An error occurred while attempting to export personal data.
Unable to generate export file. ZipArchive not available.

I'll make a PR shortly. 👍

[tianon]

#304 👍