fix-up typo unkown->unknown (#6055)
fix-up typo unkown->unknown (#6055)

Signed-off-by: chentanjun <4b3be42cf3f5b52a2a127c06f66e0403587f4fbf@qq.com>
keegancsmith/prometheus,keegancsmith/prometheus,Gouthamve/prometheus,prometheus/prometheus,GoogleCloudPlatform/prometheus,GoogleCloudPlatform/prometheus,Gouthamve/prometheus,alileza/prometheus,GoogleCloudPlatform/prometheus,alileza/prometheus,kangwoo/prometheus,GoogleCloudPlatform/prometheus,GoogleCloudPlatform/prometheus,alileza/prometheus,prometheus/prometheus,kangwoo/prometheus,keegancsmith/prometheus,prometheus/prometheus,keegancsmith/prometheus,alileza/prometheus,Gouthamve/prometheus,Gouthamve/prometheus,kangwoo/prometheus,alileza/prometheus,kangwoo/prometheus,prometheus/prometheus,keegancsmith/prometheus,prometheus/prometheus