mrhlpr.json: adjust unknown regex (!630)

Do not mark commit messages as NOK if the subject...
* has an uppercase letter (except for right after the colon)
* contains a dot or underscore before the colon

.mrhlpr.json

@@ -9,7 +9,7 @@
             "^[a-z]+/[a-z-0-9*{}]+: removed, upstreamed( \\(!\\d+\\)|)$"
         ],
         "unknown": [
-            "^[a-z-0-9*{}\\/]+: [a-z\\-0-9*{}\\(\\)\\._ ]+( \\(!\\d+\\)|)$"
+            "^[a-z-0-9_.*{}\\/]+: [a-z\\-0-9*{}\\(\\)\\._ ][A-Za-z\\-0-9*{}\\(\\)\\._ ]+( \\(!\\d+\\)|)$"
         ]
     }
 }