Update tutorial-flow.md

Author: ocots

docs/src/tutorial-flow.md

@@ -333,7 +333,7 @@ yf, pf = f(0, [x0, tf], [p0, 0], 1)
 
 !!! note "Goddard problem"
 
-    In the [Goddard problem](https://control-toolbox.org/Tutorials.jl/stable/tutorial-goddard/#tutorial-goddard-structure), you may find other constructions of flows, especially for singular and boundary arcs.
+    In the [Goddard problem](https://control-toolbox.org/Tutorials.jl/stable/tutorial-goddard.html#tutorial-goddard-structure), you may find other constructions of flows, especially for singular and boundary arcs.
 
 ## Concatenation of arcs
 
@@ -418,4 +418,4 @@ t = range(1, 5e2, 201)
 plt = plot(yaxis=:log, legend=:bottomright, title="Comparison of concatenations", xlabel="t")
 plot!(plt, t, t->abs(φ(t)-x0), label="OptimalControl")
 plot!(plt, t, t->abs(ψ(t)-x0), label="Classical")
-```
+```