Update duplex.md to use the latest string contact. (#11644)

Anduin2017 · Ron Petrusha · commit 7e1f2a014575 · 2019-04-04T08:49:58.000-07:00
* Update duplex.md to use the latest string contact.

Update duplex.md to use the latest string contact method.

* Update docs/framework/wcf/samples/duplex.md

Co-Authored-By: Anduin2017 &lt;anduin@aiursoft.com&gt;

* Update docs/framework/wcf/samples/duplex.md

Co-Authored-By: Anduin2017 &lt;anduin@aiursoft.com&gt;
diff --git a/docs/framework/wcf/samples/duplex.md b/docs/framework/wcf/samples/duplex.md
@@ -55,14 +55,14 @@ public class CalculatorService : ICalculatorDuplex
   
     public void Clear()  
     {  
-        Callback.Equation(equation + " = " + result.ToString());  
+        Callback.Equation($"{equation} = {result}");  
         equation = result.ToString();  
     }  
   
     public void AddTo(double n)  
     {  
         result += n;  
-        equation += " + " + n.ToString();  
+        equation += $" + {n}";  
         Callback.Result(result);  
     }  
     

Original file line number	Diff line number	Diff line change
`@@ -55,14 +55,14 @@ public class CalculatorService : ICalculatorDuplex`
`55`	`55`
`56`	`56`	`public void Clear()`
`57`	`57`	`{`
`58`		`- Callback.Equation(equation + " = " + result.ToString());`
	`58`	`+ Callback.Equation($"{equation} = {result}");`
`59`	`59`	`equation = result.ToString();`
`60`	`60`	`}`
`61`	`61`
`62`	`62`	`public void AddTo(double n)`
`63`	`63`	`{`
`64`	`64`	`result += n;`
`65`		`- equation += " + " + n.ToString();`
	`65`	`+ equation += $" + {n}";`
`66`	`66`	`Callback.Result(result);`
`67`	`67`	`}`
`68`	`68`