Bump log4j.version from 2.20.0 to 2.21.1 (closes #156)

Bumps `log4j.version` from 2.20.0 to 2.21.1.

Updates `org.apache.logging.log4j:log4j-api` from 2.20.0 to 2.21.1

Updates `org.apache.logging.log4j:log4j-core` from 2.20.0 to 2.21.1

Updates `org.apache.logging.log4j:log4j-slf4j-impl` from 2.20.0 to 2.21.1

Updates `org.apache.logging.log4j:log4j-jul` from 2.20.0 to 2.21.1

---
updated-dependencies:
- dependency-name: org.apache.logging.log4j:log4j-api
  dependency-type: direct:production
  update-type: version-update:semver-minor
- dependency-name: org.apache.logging.log4j:log4j-core
  dependency-type: direct:production
  update-type: version-update:semver-minor
- dependency-name: org.apache.logging.log4j:log4j-slf4j-impl
  dependency-type: direct:production
  update-type: version-update:semver-minor
- dependency-name: org.apache.logging.log4j:log4j-jul
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Change-Id: I7f5396f0c3edc6625a119d6aef40a183c5247a5b
Reviewed-on: https://korap.ids-mannheim.de/gerrit/c/KorAP/Koral/+/7687
Reviewed-by: Nils Diewald <nils@diewald-online.de>
diff --git a/pom.xml b/pom.xml
index 406df49..52bde51 100644
--- a/pom.xml
+++ b/pom.xml
@@ -43,7 +43,7 @@
 		<antlr4.version>4.9.3</antlr4.version>
 		<antlr3.version>3.5.3</antlr3.version>
 		<java.version>11</java.version>
-		<log4j.version>2.20.0</log4j.version>
+		<log4j.version>2.21.1</log4j.version>
 	</properties>
 	
 	<repositories>