resolves issue asciidoctor#258 by adding create method with classload…

…er and gempath.

asciidoctorj-core/src/main/java/org/asciidoctor/internal/JRubyAsciidoctor.java

@@ -149,8 +149,11 @@ private static Asciidoctor createJRubyAsciidoctorInstance(Map<String, Object> en
 
     private static Asciidoctor createJRubyAsciidoctorInstance(ClassLoader classloader, String gemPath) {
 
+        Map<String, Object> env = new HashMap<String, Object>();
+        env.put(GEM_PATH, gemPath);
+
         ScriptingContainer container = new ScriptingContainer();
-        setsGemPath(gemPath, container);
+        injectEnvironmentVariables(container.getProvider().getRubyInstanceConfig(), env);
         container.setClassLoader(classloader);
         Ruby rubyRuntime = container.getProvider().getRuntime();
 
@@ -164,13 +167,6 @@ private static Asciidoctor createJRubyAsciidoctorInstance(ClassLoader classloade
         return jRubyAsciidoctor;
     }
 
-    private static void setsGemPath(String gemPath, ScriptingContainer container) {
-        Map environment = container.getEnvironment();
-        Map newEnvironment = new HashMap(environment);
-        newEnvironment.put(GEM_PATH, gemPath);
-        container.setEnvironment(newEnvironment);
-    }
-
     private static void injectEnvironmentVariables(RubyInstanceConfig config, Map<String, Object> environmentVars) {
         EnvironmentInjector environmentInjector = new EnvironmentInjector(config);
         environmentInjector.inject(environmentVars);