Fix toString for Connections

Author: Zomis

src/main/groovy/net/zomis/machlearn/neural/DummyConnection.java

@@ -26,7 +26,7 @@ public void setWeight(double value) {
 
     @Override
     public String toString() {
-        return "w0 $weight";
+        return "w0 " + weight;
     }
 
 }

src/main/groovy/net/zomis/machlearn/neural/NeuronConnection.java

@@ -34,7 +34,7 @@ public static NeuronConnection create(Neuron input, Neuron output) {
 
     @Override
     public String toString() {
-        return "$from --> $to w($weight)";
+        return String.format("%s --> %s w(%f)", from, to, weight);
     }
 
     public Neuron getTo() {