Add missing quotation marks in autoloader

[kfkonrad]

Description

The auto loader lacked quotation marks around a variable. This PR fixes that and with this the bug described in #698. I tested it under both fish 2.7 and 3.0, that's also the reason why I'm attaching two environment reports.

Fixes #698

Environment report for fish 2.7

Oh My Fish version:   6
OS type:              Linux
Fish version:         fish, version 2.7.1
Git version:          git version 2.11.0
Git core.autocrlf:    no
Your shell is ready to swim.

Environment report for fish 3.0

Oh My Fish version:   6
OS type:              Darwin
Fish version:         fish, version 3.0.2
Git version:          git version 2.21.0 Git version:          hub version 2.11.2
Git core.autocrlf:    no
Your shell is ready to swim.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• New and existing tests pass locally with my changes

[derekstavis]

Confirmed this is an issue and this fixes it.