Bugfix working directory

[royalfig]

The working-directory didn't successfully upload a Ghost theme, meaning that repos with themes in subfolders couldn't use the GH Action. Ref #71

The error was with the zip command:

 await exec.exec(`zip -r ${themeZip} ${core.getInput('working-directory') || '.'} -x *.git* *.zip yarn* npm* node_modules* *routes.yaml *redirects.yaml *redirects.json ${exclude}`, [], {cwd: basePath});

The issue here is that the command would generate this file structure, where required files wouldn't be in the root of the folder.

archive.zip
│
└───theme
    │   file1.hbs
    │   file2.hbs
    │
    └───subfolder
        │   file3.hbs
        │   ...

In investigating the code, it also become clear that Action wouldn't pull the right theme name. The PR updates the basepath to align with the working-directory when present, otherwise, it defaults to ., as before.

---

ref #71