Fix subject name detection for moduleFor('type:name').

Previously, when no `options` were detected the `subject` was not set,
causing issues later when we try to process `this.subject()` statements.

Author: Robert Jackson

__testfixtures__/ember-qunit-codemod/subject.input.js

@@ -77,3 +77,9 @@ moduleFor('service:foo', 'Unit | Service | Foo', {
 test('can use service', function (assert) {
   this.service.something();
 });
+
+moduleFor('service:foo');
+
+test('does not require more than one argument', function(assert) {
+  let suject = this.subject();
+});

__testfixtures__/ember-qunit-codemod/subject.output.js

@@ -82,3 +82,11 @@ module('Unit | Service | Foo', function(hooks) {
     this.service.something();
   });
 });
+
+module('service:foo', function(hooks) {
+  setupTest(hooks);
+
+  test('does not require more than one argument', function(assert) {
+    let subject = this.owner.factoryFor('component:foo-bar').create();
+  });
+});

ember-qunit-codemod.js

@@ -110,7 +110,7 @@ module.exports = function(file, api, options) {
     if (lastArgument.type === 'ObjectExpression') {
       options = calleeArguments.pop();
     }
-    moduleName = calleeArguments[1] || calleeArguments[0];
+    subject = moduleName = calleeArguments[1] || calleeArguments[0];
 
     let setupIdentifier = 'setupTest';
     if (options) {