baseDir = "\${XDG_RUNTIME_DIR}" seems to cause an error in fish

``` ~/.config/fish/functions/xxx.fish (line 4): Variables cannot be bracketed. In fish, please use {$XDG_RUNTIME_DIR}. cat ${XDG_RUNTIME_DIR}/agenix/test ^ ``` Since the above error occurs, would it make sense to provide `baseDir` as a configuration option?"