Bump default graal version to 20.2.0 (#396)

* Bump default graal version to 20.2.0

This fixes a problem with projects that make use of the kotlin coroutines.
More details: oracle/graal#366

* Add changelog

README.md

@@ -23,7 +23,7 @@ Configuration
 Configure this plugin and its wrappers around GraalVM tools through the `graal` extension with the following options:
 
 **General GraalVM controls**
-* `graalVersion`: the version string to use when downloading GraalVM (defaults to `20.0.0`)
+* `graalVersion`: the version string to use when downloading GraalVM (defaults to `20.2.0`)
 * `downloadBaseUrl`: the base download URL to use (defaults to `https://github.com/oracle/graal/releases/download/`)
 * `javaVersion`: the Java version to use (can be either `8` or `11`, defaults to `8`)
     * for `8`: Windows SDK 7.1 will be used (`C:\Program Files\Microsoft SDKs\Windows\v7.1\Bin\SetEnv.cmd`)

changelog/@unreleased/pr-396.v2.yml

@@ -0,0 +1,5 @@
+type: improvement
+improvement:
+  description: Bump default graal version to 20.2.0
+  links:
+    - https://github.com/palantir/gradle-graal/pull/396

src/main/java/com/palantir/gradle/graal/GraalExtension.java

@@ -43,7 +43,7 @@ public class GraalExtension {
     private static final String DEFAULT_DOWNLOAD_BASE_URL = "https://github.com/oracle/graal/releases/download/";
     private static final String DOWNLOAD_BASE_URL_GRAAL_19_3 =
             "https://github.com/graalvm/graalvm-ce-builds/" + "releases/download/";
-    private static final String DEFAULT_GRAAL_VERSION = "20.0.0";
+    private static final String DEFAULT_GRAAL_VERSION = "20.2.0";
     private static final List<String> SUPPORTED_JAVA_VERSIONS = Arrays.asList("11", "8");
     private static final String DEFAULT_JAVA_VERSION = "8";