Fix grammar in CONTRIBUTING.md
Fix grammar in CONTRIBUTING.md

GFriedrich/logging-log4j2,xnslong/logging-log4j2,xnslong/logging-log4j2,GFriedrich/logging-log4j2,apache/logging-log4j2,codescale/logging-log4j2,codescale/logging-log4j2,apache/logging-log4j2,xnslong/logging-log4j2,GFriedrich/logging-log4j2,codescale/logging-log4j2,apache/logging-log4j2