Fix another stupid copy-and-paste bug. Thanks to @thomasrarris. Closes #17.

Author: m8pple

include/puzzler/puzzles/heat_world.hpp

@@ -145,6 +145,7 @@ namespace puzzler
 
               res=std::min(1.0f, std::max(-1.0f, res));
 
+	      buffer[index] = res;
             }
           }
         }