add sample code

Author: SpaceWhite

java/ql/src/Security/CWE/CWE-094/ScriptEngine.java

@@ -0,0 +1,4 @@
+// Bad: arbitrary code execution
+ScriptEngineManager scriptEngineManager = new ScriptEngineManager();
+ScriptEngine scriptEngine = scriptEngineManager.getEngineByExtension("js");
+Object result = scriptEngine.eval(code);