Fix jenkins credetials interpolation

Change-Id: I7327879a90c4ad00afb962164353f35c2f6a1ce0
diff --git a/_states/jenkins_credential.py b/_states/jenkins_credential.py
index 0a6287a..3009673 100644
--- a/_states/jenkins_credential.py
+++ b/_states/jenkins_credential.py
@@ -36,7 +36,7 @@
     )[0].getStore()
 
     credentials_new = new ${clazz}(
-      {params}
+      ${params}
     )
     // remove credentails with same if before created new one, if exists
     def existingCreds = com.cloudbees.plugins.credentials.CredentialsProvider.lookupCredentials(