Update Dockerfile

Dockerfile

@@ -1,4 +1,4 @@
-FROM fithwum/debian-base
+FROM fithwum/debian-base:stretch
 MAINTAINER fithwum
 
 ENV ACCEPT_EULA="false"
@@ -9,7 +9,7 @@ ARG INSTALL_SCRIPT=https://raw.githubusercontent.com/fithwum/minecraft/master/fi
 
 # Install java8 & dependencies.
 RUN apt-get -y update \
-	&& apt-get install -y default-jre ca-certificates-java \
+	&& apt-get install -y openjdk-8-jdk ca-certificates-java \
 	&& apt-get clean && rm -rf /var/lib/apt/lists/*\
 	&& update-ca-certificates -f;