bullet: Fix BulletHeightfieldShape::fillin

Closes #860

panda/src/bullet/bulletHeightfieldShape.cxx

@@ -200,7 +200,7 @@ fillin(DatagramIterator &scan, BamReader *manager) {
 
   size_t size = (size_t)_num_rows * (size_t)_num_cols;
   delete [] _data;
-  _data = new float[size];
+  _data = new btScalar[size];
 
   for (size_t i = 0; i < size; ++i) {
     _data[i]  = scan.get_stdfloat();