fix: get oneListGroup to work as expected for array of strings

If I have `oneListGroup` enabled I would expect that:

```json
{
  a: ['(first)', 'second']
}
```

Would give me:
```xml
<a>(first)(second)</a>
```

But I get:
```xml
<a>
  <a>(first)</a>
  <a>(second)</a>
</a>
```

This commit fixes that issue.

spec/j2x_spec.js

@@ -482,7 +482,20 @@ describe("XMLBuilder", function() {
         const expected = `<a><b>1</b><b>2</b></a>`;
         expect(result).toEqual(expected);
     });
-
+
+    it("should correctly handle values with oneListGroup", function() {
+        const jObj = {
+            "a": [
+                "(first)",
+                "(second)"
+            ],
+        };
+        const builder = new XMLBuilder({oneListGroup:"true", attributesGroupName: "@"});
+        const result = builder.build(jObj);
+        const expected = `<a>(first)(second)</a>`;
+        expect(result).toEqual(expected);
+    });
+
     it('should build tag with only text node', async () => {
         const schema_obj = {
           field: {

src/xmlbuilder/json2xml.js

@@ -130,7 +130,13 @@ Builder.prototype.j2x = function(jObj, level) {
             listTagVal += this.processTextOrObjNode(item, key, level)
           }
         } else {
-          listTagVal += this.buildTextValNode(item, key, '', level);
+          if (this.options.oneListGroup) {
+            let textValue = this.options.tagValueProcessor(key, item);
+            textValue = this.replaceEntitiesValue(textValue);
+            listTagVal += textValue;
+          } else {
+            listTagVal += this.buildTextValNode(item, key, '', level);
+          }
         }
       }
       if(this.options.oneListGroup){