minor bug in slice

Former-commit-id: 6f17f646fb3b8a1970f11328cfc53311f123958e

slice.h

@@ -80,7 +80,7 @@ inline void igl::slice(
     dyn_Y(ym,yn);
   // Take a guess at the number of nonzeros (this assumes uniform distribution
   // not banded or heavily diagonal)
-  dyn_Y.reserve((X.nonzeros()/(X.rows()*X.cols())) * (ym*yn));
+  dyn_Y.reserve((X.nonZeros()/(X.rows()*X.cols())) * (ym*yn));
   // Iterate over outside
   for(int k=0; k<X.outerSize(); ++k)
   {