books: update copyright notice to 2019

Steve Hollasch · hollasch · commit d1e48b2326ac · 2019-10-07T22:10:31.000Z
diff --git a/books/RayTracingInOneWeekend.html b/books/RayTracingInOneWeekend.html
@@ -6,7 +6,7 @@
                                    **Ray Tracing in One Weekend**
                                            Peter Shirley
                                             Version 1.54
-                      <br>Copyright 2018. Peter Shirley. All rights reserved.
+                    <br>Copyright 2018-2019. Peter Shirley. All rights reserved.
 
 
 
diff --git a/books/RayTracingTheNextWeek.html b/books/RayTracingTheNextWeek.html
@@ -6,7 +6,7 @@
                                    **Ray Tracing: The Next Week**
                                            Peter Shirley
                                             Version 1.41
-                      <br>Copyright 2018. Peter Shirley. All rights reserved.
+                    <br>Copyright 2018-2019. Peter Shirley. All rights reserved.
 
 
 
diff --git a/books/RayTracingTheRestOfYourLife.html b/books/RayTracingTheRestOfYourLife.html
@@ -6,7 +6,7 @@
                                **Ray Tracing: The Rest of Your Life**
                                            Peter Shirley
                                            Version 1.123
-                      <br>Copyright 2018. Peter Shirley. All rights reserved.
+                    <br>Copyright 2018-2019. Peter Shirley. All rights reserved.
 
 
 
