Fix formatting by adding a newline at the end of ProxyTest.cs

Author: iampopovich

dotnet/test/common/ProxyTest.cs

@@ -327,4 +327,4 @@ public void ConstructingWithNullKeysWorksAsExpected()
         Assert.That(proxy.IsAutoDetect, Is.False);
         Assert.That(proxy.HttpProxy, Is.EqualTo("http://www.example.com"));
     }
-}
+}