jenkins: fixed replacement of version string

Signed-off-by: Marc Mattmueller <marc.mattmueller@netmodule.com>

Jenkinsfile

@@ -96,8 +96,9 @@ def build_version(versionParam) {
   }
   gitversion = sh(returnStdout: true, script: "${gitCmd}").trim()
   String[] versionArr = "${gitversion}".split("-")
-  if("${versionParam}" != "") {  
-    versionArr[0] = "${versionParam}"
+  if(versionParam != '') {
+    String newVersionStr = versionParam 
+    versionArr[0] = newVersionStr
   }
   rlsVersion = versionArr.join("-")
   return rlsVersion