fiji.toml: give full path to fiji.py

It matters on macOS, which has a CWD of ${app-dir}/Contents/MacOS rather
than ${app-dir} during launch. (This CWD behavior might be undesirable,
but it's good to be explicit with the script-path anyway.)

configs/fiji.toml

@@ -104,7 +104,7 @@ python.packages = [
   'scyjava>=1.9.1',
 ]
 
-python.script-path = ['fiji.py']
+python.script-path = ['${app-dir}/fiji.py']
 
 python.main-args = [
     '${jvm.libjvmPath}',