Correct geometry from vec3 to point3 final scene

Book 1, we were computing the length of a point - vector, but that
doesn't make sense; it should have been computing the length of the
point - point.

Resolves #609

Author: hollasch

CHANGELOG.md

@@ -3,8 +3,11 @@ Change Log -- Ray Tracing in One Weekend
 
 # v3.1.2 (in progress)
 
+### _In One Weekend_
+  - Fix: Corrected geometry type when computing distance between two points, final scene (#609)
+
 ### _The Rest of Your Life_
-  - Fix: missing closing parenthesis in listing 10 (#603)
+  - Fix: Missing closing parenthesis in listing 10 (#603)
 
 
 ----------------------------------------------------------------------------------------------------

books/RayTracingInOneWeekend.html

@@ -2889,7 +2889,7 @@
                 auto choose_mat = random_double();
                 point3 center(a + 0.9*random_double(), 0.2, b + 0.9*random_double());
 
-                if ((center - vec3(4, 0.2, 0)).length() > 0.9) {
+                if ((center - point3(4, 0.2, 0)).length() > 0.9) {
                     shared_ptr<material> sphere_material;
 
                     if (choose_mat < 0.8) {

src/InOneWeekend/main.cc

@@ -52,7 +52,7 @@ hittable_list random_scene() {
             auto choose_mat = random_double();
             point3 center(a + 0.9*random_double(), 0.2, b + 0.9*random_double());
 
-            if ((center - vec3(4, 0.2, 0)).length() > 0.9) {
+            if ((center - point3(4, 0.2, 0)).length() > 0.9) {
                 shared_ptr<material> sphere_material;
 
                 if (choose_mat < 0.8) {