Removed cmath dependency.

plane.cpp

@@ -1,16 +1,14 @@
-#include <cmath>
-
 #include "plane.hpp"
 
 #define TOL 1e-6
 
-using std::fabs;
+using glm::abs;
 using glm::dot;
 
 bool Plane::intersect(Ray & r, float & t) const {
   float d = dot(r.m_direction, m_normal);
 
-  if (fabs(d) > TOL) {
+  if (abs(d) > TOL) {
     t = dot(m_normal, (m_point - r.m_origin)) / d;
     return t >= 0.0f;
   }