Fix: Change Len to lenSq in projection - Update vec3.cpp

[exequielpagliari]

I detected a type error in the book and repository. The author used Length instead of SqrLength in the implementation shown in the book.

Author's implementation:

vec3 project(const vec3 &a, const vec3 &b) {
 float magBSq = len(b);
 if (magBSq < VEC3_EPSILON) {
  return vec3();
 }
 float scale = dot(a, b) / magBSq;
 return b * scale;
}

Vector projection formula (A . B / |B|^2) * B

LenSq is the calculation of the hypotenuse without radically dividing, so it can be represented as |B| ^ 2