Use caller class class loader instead of context class loader. Fixes #25

Author: glibas

groovy/src/main/java/io/cucumber/groovy/GroovyBackend.java

@@ -53,9 +53,9 @@ static GroovyBackend getInstance() {
         return instanceThreadLocal.get();
     }
 
-    private static GroovyShell createShell() {
+    private GroovyShell createShell() {
         CompilerConfiguration compilerConfig = new CompilerConfiguration();
-        return new GroovyShell(Thread.currentThread().getContextClassLoader(), new Binding(), compilerConfig);
+        return new GroovyShell(this.getClass().getClassLoader(), new Binding(), compilerConfig);
     }