Bug fix in igl::grad_tri(uniform)

Former-commit-id: ea54390dc2297a79b53897f4a5636944bb3d1157

include/igl/grad.cpp

@@ -149,7 +149,7 @@ IGL_INLINE void grad_tri(const Eigen::PlainObjectBase<DerivedV>&V,
       // get h (by the area of the triangle)
       double h = sqrt( (dblA)/sin(M_PI / 3.0)); // (h^2*sin(60))/2. = Area => h = sqrt(2*Area/sin_60)
 
-      Eigen::VectorXd v1,v2,v3;
+      Eigen::Vector3d v1,v2,v3;
       v1 << 0,0,0;
       v2 << h,0,0;
       v3 << h/2.,(sqrt(3)/2.)*h,0;