8030793: Update jprt.properties to release jdk9

Reviewed-by: chegar
diff --git a/make/jprt.properties b/make/jprt.properties
index 2adc170..081ac7e 100644
--- a/make/jprt.properties
+++ b/make/jprt.properties
@@ -26,7 +26,7 @@
 # Properties for jprt
 
 # Locked down to jdk8
-jprt.tools.default.release=jdk8
+jprt.tools.default.release=jdk9
 
 # Unix toolkit to use for building on windows
 jprt.windows.jdk8.build.unix.toolkit=cygwin