Wrong icon for xslt+xml

[gtnewton]

• Distribution (version): Ubuntu 18.04
• Desktop environment: GNOME
• Installing method: PPA

Issue
The icon for the xslt+xml mimetype (application-xslt+xml.svg) is an alias to the spreadsheet icon (x-office-spreadsheet.svg).

It should point to application-xml.svg instead.

This problem exists in the PPA and the current git version