Update modelingtoolkit.md

Author: ChrisRackauckas

docs/src/tutorials/modelingtoolkit.md

@@ -13,7 +13,7 @@ using ModelingToolkit, NonlinearSolve
 
 # Define a nonlinear system
 eqs = [0 ~ σ * (y - x), 0 ~ x * (ρ - z) - y, 0 ~ x * y - β * z]
-@named ns = NonlinearSystem(eqs, [x, y, z], [σ, ρ, β])
+@mtkbuild ns = NonlinearSystem(eqs, [x, y, z], [σ, ρ, β])
 
 u0 = [x => 1.0, y => 0.0, z => 0.0]