fix typho in cookicutter template generator

Change-Id: I4888872e00be01ad02bbc013a6dbda1c47229906
diff --git a/src/com/mirantis/mk/Python.groovy b/src/com/mirantis/mk/Python.groovy
index b9e79b2..1844d42 100644
--- a/src/com/mirantis/mk/Python.groovy
+++ b/src/com/mirantis/mk/Python.groovy
@@ -230,7 +230,7 @@
     configFile = "default_config.yaml"
     configString = "default_context:\n"
     for (parameter in context) {
-      configStringString = "${configString}  ${parameter.key}: ${parameter.value}\n"
+      configString = "${configString}  ${parameter.key}: ${parameter.value}\n"
     }
     writeFile file: configFile, text: configString
     command = ". ${path}/bin/activate; cookiecutter --config-file ${configFile} --output-dir ${outputDir} --overwrite-if-exists --verbose --no-input ${template}"