Favicon generator not handling paths well

The favicon generator is not handling paths correctly. It seems to be assuming/requiring relative paths only, and not allowing for absolute paths.

For example, running the following from my project directory didn't work:
```
unthink gen favicon ~/Downloads/my_icon.png
```
It fails with the "cannot find source image" error.

And doing the following from the directory the image was in didn't work (in a different way):
```
unthink gen favicon ./my_icon.png ~/Projects/my-project-directory/src/public/images
```
This resulted in the files being generated in the following location (I ran the command from my Downloads folder):
```
/Users/dan.alexander/Downloads/Users/dan.alexander/Projects/my-project-directory/src/public/images
```
It's only treating the target path as relative.