fix: Fix bug in logic on listing 5.20 (#772)

Fixes #728

By happenstance of default value being 0 and that being the value of
Black, test was passing. Changed to yellow to make it clear that this
failed

Errata.md

@@ -33,4 +33,5 @@ Zhou Jing | 20 | 1018 | Change paragraph beginning with "The need to support TAP
 Zhou Jing | 18 | 911 | Change CommandLineRequiredAttribute to CommandLineSwitchRequiredAttribute
 Zhou Jing | 18 | 902-903 | Change CommandLineAliasAttribute to CommandLineSwitchAliasAttribute
 Zhou Jing | 23 | 1105 | Change `Length = 10` in listing 23.20 to `Length = 12` to show entire output message
-Zhou Jing | 18 | 926-927 | Change 'LastName' references to be 'FirstName' in paragraphs
+Zhou Jing | 18 | 926-927 | Change 'LastName' references to be 'FirstName' in paragraphs
+Jinhang He | 5 | 255 | Edit listing 5.20 to used `image[index]` for the second print statement

src/Chapter05.Tests/Listing05.20.ReturningAReference.Tests.cs

@@ -8,12 +8,9 @@ public class ProgramTests
     public void Main_InputInigoMontoya_WriteFullName()
     {
         string expected = @"image\[*\]=Red
-image\[*\]=Black";
+image\[*\]=Yellow";
 
-        IntelliTect.TestTools.Console.ConsoleAssert.ExpectLike(expected,
-        () =>
-        {
-            Program.Main();
-        });
+        IntelliTect.TestTools.Console.ConsoleAssert.ExpectLike(expected, 
+            () => Program.Main());
     }
 }

src/Chapter05/Listing05.20.ReturningAReference.cs

@@ -32,11 +32,11 @@ public static void Main()
         #region HIGHLIGHT
         // Obtain a reference to the first red pixel
         ref byte redPixel = ref FindFirstRedEyePixel(image);
-        // Update it to be Black
-        redPixel = (byte)ConsoleColor.Black;
+        // Update it to be Yellow
+        redPixel = (byte)ConsoleColor.Yellow;
         #endregion HIGHLIGHT
         Console.WriteLine(
-            $"image[{index}]={(ConsoleColor)image[redPixel]}");
+            $"image[{index}]={(ConsoleColor)image[index]}");
     }
     #endregion INCLUDE
 }