Add missing backslash to pipeline stage regex (#19)

Author: efemiydi

docker-compose.yaml

@@ -7,7 +7,7 @@ x-logging: &default-logging
           firstline: '^\d{4}-\d{2}-\d{2} \d{1,2}:\d{2}:\d{2}'
           max_wait_time: 3s
       - regex:
-          expression: '^(?P<time>\d{4}-\d{2}-\d{2} \d{1,2}:\d{2}:\d{2},d{3}) (?P<message>(?s:.*))$$'
+          expression: '^(?P<time>\d{4}-\d{2}-\d{2} \d{1,2}:\d{2}:\d{2},\d{3}) (?P<message>(?s:.*))$$'
 
 version: "3.4"