Fixes strategy that finds out if running on a JVM older than JDK8.

JDK9 defines a new numbering scheme for its version, it no longer
follows the 1.x format. JDK9 uses 9.x.y.z instead.

Fixes groovyfx-project#52

src/main/groovy/groovyx/javafx/JdkUtil.groovy

@@ -17,6 +17,11 @@ package groovyx.javafx
 
 class JdkUtil {
     static boolean jdkIsBefore8() {
-        System.properties['java.version'][0..2].toFloat() < 1.8f
+        String version = System.properties['java.version']
+        if (version.startsWith('1')) {
+            version[0..2].toFloat() < 1.8f
+        } else {
+            false
+        }
     }
 }