fix C# 6 build

Author: mythz

tests/ServiceStack.Text.Tests/JsonTests/CustomSerializerTests.cs

@@ -319,16 +319,19 @@ public class DcStatus
             [Format("{0:0.000} A")]
             public Double Current { get; set; }
             [Format("{0:0} W")]
-            public Double Power => Voltage * Current;
+            public Double Power
+            {
+                get { return Voltage * Current; }
+            }
 
             public string ToJson()
             {
                 return new Dictionary<string, string>
-            {
-                { "Voltage", "{0:0.0} V".Fmt(Voltage) },
-                { "Current", "{0:0.000} A".Fmt(Current) },
-                { "Power", "{0:0} W".Fmt(Power) },
-            }.ToJson();
+                {
+                    { "Voltage", "{0:0.0} V".Fmt(Voltage) },
+                    { "Current", "{0:0.000} A".Fmt(Current) },
+                    { "Power", "{0:0} W".Fmt(Power) },
+                }.ToJson();
             }
         }
 
@@ -339,7 +342,10 @@ public class DcStatus2
             [Format("{0:0.000} A")]
             public Double Current { get; set; }
             [Format("{0:0} W")]
-            public Double Power => Voltage * Current;
+            public Double Power
+            {
+                get { return Voltage*Current; }
+            }
         }
 
         [Test]