Update Build Section to Require JDK 11

Closes gh-9418

README.adoc

@@ -30,9 +30,9 @@ In the instructions below, https://vimeo.com/34436402[`./gradlew`] is invoked fr
 a cross-platform, self-contained bootstrap mechanism for the build.
 
 === Prerequisites
-https://help.github.com/set-up-git-redirect[Git] and the https://www.oracle.com/technetwork/java/javase/downloads[JDK8 build].
+https://help.github.com/set-up-git-redirect[Git] and the https://www.oracle.com/technetwork/java/javase/downloads[JDK11 build].
 
-Be sure that your `JAVA_HOME` environment variable points to the `jdk1.8.0` folder extracted from the JDK download.
+Be sure that your `JAVA_HOME` environment variable points to the `jdk-11` folder extracted from the JDK download.
 
 === Check out sources
 [indent=0]