update base image to openjdk:15.0.2-jdk-slim-buster and replace apt commands with apt-get (hadolint recommandations)
update base image to openjdk:15.0.2-jdk-slim-buster and replace apt commands with apt-get (hadolint recommandations)

dadoonet/fscrawler,dadoonet/fscrawler,dadoonet/fscrawler