Merge branch 'v2.1-dev' into 'v2.x-master'

Cleanup based on gradle:6-jdk11 image

See merge request !13

.gitlab-ci.yml

-image: openjdk:11-jdk
+image: gradle:6-jdk11
 
 variables:
-  GRADLE_OPTS: "-Dorg.gradle.daemon=false"
   NEXUS_CREDENTIALS: "-Pnexususer=$NEXUS_REPO_USER -Pnexuspass=$NEXUS_REPO_PASS"
 
-before_script:
-  - export GRADLE_USER_HOME=`pwd`/.gradle
-  - ./gradlew wrapper --distribution-type=bin
-
-cache:
-  paths:
-    - .gradle/wrapper
-    - .gradle/caches
-
 stages:
   - test
   - build
@@ -21,11 +11,11 @@ stages:
 test:
   stage: test
   script:
-    - ./gradlew check
+    - gradle check
 
 build:
   stage: build
-  script: ./gradlew assemble
+  script: gradle assemble
   artifacts:
     paths:
       - dariahsp-core/build/libs/*.jar
@@ -36,6 +26,6 @@ build:
 deploy:
   stage: deploy
   script: 
-    - ./gradlew publish -x test $NEXUS_CREDENTIALS
+    - gradle publish -x test $NEXUS_CREDENTIALS
   only:
     - v2.x-master