update sde example

Author: TorkelE

README.md

@@ -201,7 +201,7 @@ In this case, we would instead like to perform stochastic simulations, so we tra
 ```julia
 u0 = [:V => 25.0, :G => 50.0, :Gᴾ => 0.0]
 tspan = (0.0, 20.0)
-ps = [:Vₘ => 50.0, :g => 0.2, :kₚ => 100.0, :kᵢ => 60.0]
+ps = [:Vₘ => 50.0, :g => 0.3, :kₚ => 100.0, :kᵢ => 60.0]
 sprob = SDEProblem(cell_model, u0, tspan, ps)
 ```
 This produces the following equations: