Add <code> style to 'nil' and Remove redundant space

examples/errors/errors.go

@@ -23,7 +23,7 @@ func f1(arg int) (int, error) {
 
     }
 
-    // A nil value in the error position indicates that
+    // A `nil` value in the error position indicates that
     // there was no error.
     return arg + 3, nil
 }