Update README for Java 11 (#3464)

diff --git a/README.md b/README.md
index 1fcc3d9..6d43483 100644
--- a/README.md
+++ b/README.md
@@ -29,7 +29,7 @@
 [https://heron.incubator.apache.org/](https://heron.incubator.apache.org/)
 
 #### Heron Requirements:
- * Java JDK 1.8
+ * Java 11
  * Python 3
  * Bazel 0.26.0