Allow for sites with YAML/JSON configuration

[tdemin]

gmnhg will as of now disregard Hugo sites configured with either YAML (config.yaml) or JSON (config.json), despite upstream Hugo allowing for this.

gmnhg/cmd/gmnhg/main.go

Line 169 in e5d7911

if fileInfo, err := os.Stat("config.toml"); os.IsNotExist(err) || fileInfo.IsDir() {