Use GraalVM 20.0.0 dev builds

See gh-45

Dockerfile

@@ -9,8 +9,8 @@ FROM oraclelinux:7-slim
 #       E.g.:  docker build --build-arg "https_proxy=..." --build-arg "http_proxy=..." --build-arg "no_proxy=..." ...
 
 ARG MAVEN_VERSION=3.5.3
-ARG GRAALVM_VERSION=20.1.0-dev
-ARG GRAALVM_BUILD=20200125-1203
+ARG GRAALVM_VERSION=20.0.0-dev
+ARG GRAALVM_BUILD=20200121-1000
 ARG JAVA_VERSION=java8
 ARG GRAALVM_FILE=graalvm-ce-${JAVA_VERSION}-linux-amd64-${GRAALVM_VERSION}.tar.gz
 ARG GRAALVM_PKG=https://github.com/graalvm/graalvm-ce-dev-builds/releases/download/${GRAALVM_VERSION}_${GRAALVM_BUILD}/${GRAALVM_FILE}

README.md

@@ -9,7 +9,7 @@ Once built, native images have very fast startup!
 
 This feature supports:
 
-- GraalVM 20.1 dev builds
+- GraalVM 20.0.0 dev builds
 - Spring Boot 2.3.0.M1
 
 ## Build

docker.sh

@@ -1,3 +1,3 @@
 #!/usr/bin/env bash
 
-docker run -v `pwd`:/home -it --entrypoint /bin/bash springci/graalvm-ce-java8:20.1.0-dev_20200125-1203
+docker run -v `pwd`:/home -it --entrypoint /bin/bash springci/graalvm-ce-java8:20.0.0-dev_20200121-1000