Use the latest version of Maven available on RedHat 8

Cf. https://forum.orekit.org/t/expired-ssl-certificate/1386/16

.gitlab-ci.yml

@@ -5,7 +5,7 @@ stages:
 
 default:
   # Default image
-  image: registry.orekit.org/orekit/ci-utils/maven:3.6.3-openjdk-8-slim
+  image: registry.orekit.org/orekit/ci-utils/maven:3.6.2-jdk-8-slim
   # Cache downloaded dependencies and plugins between builds.
   # To keep cache across branches add 'key: "$CI_JOB_REF_NAME"'
   cache: