Fix index increment in Signature validation

Due to the fixed index (index = 0), always the first capturing group is selected.  This was creating a problem when the signature had different types parameters.

Author: Advaitva

src/main/java/com/dashjoin/jsonata/utils/Signature.java

@@ -391,6 +391,7 @@ public Object validate(Object _args, Object context) {
                         }
                     }
                 }
+                index++;
             }
             return validatedArgs;
         }