[SDC-39] fix Function args toString

Change-Id: I7b5d1445c701f7a18ebd5522fbf20b8cb5befc3b
Signed-off-by: Pavel Aharoni <pa0916@att.com>
diff --git a/src/main/java/org/openecomp/sdc/toscaparser/api/functions/Function.java b/src/main/java/org/openecomp/sdc/toscaparser/api/functions/Function.java
index 5e5f31f..9c39b30 100644
--- a/src/main/java/org/openecomp/sdc/toscaparser/api/functions/Function.java
+++ b/src/main/java/org/openecomp/sdc/toscaparser/api/functions/Function.java
@@ -134,7 +134,8 @@
 
 	@Override
 	public String toString() {
-		return name + ":" + args.toString();
+		String argsStr = args.size() > 1 ? args.toString() : args.get(0).toString();
+		return name + ":" + argsStr;
 	}
 }