Travis: Fix build errors

.travis.yml

@@ -1,25 +1,45 @@
 language: android
+dist: trusty
 android:
   components:
     - android-9
 jdk:
-  - oraclejdk8
+  - openjdk8
-sudo: false
+  - openjdk11
+
+before_cache:
+  - rm -f  $HOME/.gradle/caches/modules-2/modules-2.lock
+  - rm -fr $HOME/.gradle/caches/*/plugin-resolution/
 cache:
   directories:
+    - $HOME/.gradle/caches/
+    - $HOME/.android/build-cache
     - $HOME/.m2
 
 before_install:
-  - export GRADLE_VERSION=5.4.1
+  - export GRADLE_VERSION=6.2
   - wget https://services.gradle.org/distributions/gradle-${GRADLE_VERSION}-all.zip
   - unzip -q gradle-${GRADLE_VERSION}-all.zip
   - export PATH="$(pwd)/gradle-${GRADLE_VERSION}/bin:$PATH"
 
 install: gradle assemble --stacktrace
-script: gradle check --stacktrace
+
+# Run the test suite and also install the artifacts in the local maven
+# archive to additionaly test if artifact creation is
+# functional. Which hasn't always be the case in the past, see
+# 90cbcaebc7a89f4f771f733a33ac9f389df85be2
+# Also run javadocAll to ensure it works.
+script:
+  - |
+    JAVAC_MAJOR_VERSION=$(javac -version | sed -E 's/javac ([[:digit:]]+).*/\1/')
+    GRADLE_TASKS=()
+    GRADLE_TASKS+=(check)
+    if [[ ${JAVAC_MAJOR_VERSION} -ge 11 ]]; then
+      GRADLE_TASKS+=(javadocAll)
+    fi
+    gradle ${GRADLE_TASKS[@]} --stacktrace
 
 after_success:
   - JAVAC_VERSION=$((javac -version) 2>&1)
   # Only run jacocoRootReport in the Java 8 build
   - if [[ "$JAVAC_VERSION" = javac\ 1.8.* ]]; then gradle jacocoRootReport coveralls; fi
-