Adding xml version data to body if not present

- When content is text/xml and the provided body or example does not contain the version data it will be added at the beginning.

lib/schemaUtils.js

@@ -1932,7 +1932,18 @@ module.exports = {
       else {
         bodyData = this.convertToPmBodyData(contentObj[bodyType], requestType, bodyType,
           PARAMETER_SOURCE.REQUEST, options.indentCharacter, components, options, schemaCache);
-
+        let getXmlVersionContent = (bodyContent) => {
+          const regExp = new RegExp('([<\\?xml]+[\\s{1,}]+[version="\\d.\\d"]+[\\sencoding="]+.{1,15}"\\?>)');
+          let xmlBody = bodyContent;
+          if (!bodyContent.match(regExp)) {
+            const versionContent = '<?xml version="1.0" encoding="utf-8"?>';
+            xmlBody = versionContent + xmlBody;
+          }
+          return xmlBody;
+        };
+        bodyData = bodyType === TEXT_XML ?
+          getXmlVersionContent(bodyData) :
+          bodyData;
         updateOptions = {
           mode: rDataMode,
           raw: bodyType !== APP_JSON ?