Bump maven-core in /plugins/maven/graphql-java-codegen-maven-plugin (#623)

Bumps [maven-core](https://github.com/apache/maven) from 3.6.3 to 3.8.1.
- [Release notes](https://github.com/apache/maven/releases)
- [Commits](apache/maven@maven-3.6.3...maven-3.8.1)

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Bogdan Kobylynskyi <92bogdan@gmail.com>

Author: dependabot[bot]

plugins/maven/graphql-java-codegen-maven-plugin/pom.xml

@@ -57,7 +57,7 @@
 
     <properties>
         <version.maven-plugin-api>3.6.3</version.maven-plugin-api>
-        <version.maven-core>3.6.3</version.maven-core>
+        <version.maven-core>3.8.1</version.maven-core>
         <version.maven-plugin-annotations>3.6.1</version.maven-plugin-annotations>
         <version.maven-plugin-plugin>3.6.1</version.maven-plugin-plugin>
         <version.maven-compiler-plugin>3.8.1</version.maven-compiler-plugin>