Merge branch 'gitlab-ci' into 'master'

Gitlab CI

See merge request ongresinc/pgio!9

.gitlab-ci.yml

+image: oracle/graalvm-ce:1.0.0-rc11
+
+before_script:
+  - curl "https://www-us.apache.org/dist/maven/maven-3/3.6.0/binaries/apache-maven-3.6.0-bin.tar.gz" -o apache-maven-3.6.0-bin.tar.gz 
+
+build:
+  only:
+    - tags
+  variables:
+    GRAALVM_HOME: /opt/graalvm-ce-1.0.0-rc11
+  script:
+    - tar xzf apache-maven-3.6.0-bin.tar.gz
+    - apache-maven-3.6.0/bin/mvn clean package -f /builds/ongresinc/pgio/pom.xml -P safer,assembler,executable
+    - cp /builds/ongresinc/pgio/main/target/dist/bin/pgio-* /builds/ongresinc/pgio/pgio
+  artifacts:
+    paths:
+      - /builds/ongresinc/pgio/pgio
+    name: pgio