Fix camera declaration, undefined vup variable

Resolves #686

Author: hollasch

CHANGELOG.md

@@ -5,6 +5,7 @@ Change Log -- Ray Tracing in One Weekend
 
 ### _In One Weekend_
   - Fix: replace old anti-alias result image with before-and-after image (#679)
+  - Fix: undefined `vup` variable in camera definition (#686)
 
 ### _The Next Week_
   - Delete: remove unused u,v,w variables in initial `perlin::noise()` function (#684)

books/RayTracingInOneWeekend.html

@@ -2848,7 +2848,7 @@
 And we can change field of view:
 
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ C++
-    camera cam(point3(-2,2,1), point3(0,0,-1), vup, 20, aspect_ratio);
+    camera cam(point3(-2,2,1), point3(0,0,-1), vec3(0,1,0), 20, aspect_ratio);
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     [Listing [change-field-view]: <kbd>[main.cc]</kbd> Change field of view]