Update src/ode/ode_simple_nonlinear_prob.jl

Author: mforets

src/ode/ode_simple_nonlinear_prob.jl

@@ -283,7 +283,7 @@ y₆(0) = -4
 y₇(0) = 4
 ```
 
-and with ``\\frac{dxᵢ(0)}{dt}=\frac{dyᵢ(0)}{dt}=0`` except for
+and with ``\\frac{dxᵢ(0)}{dt}=\\frac{dyᵢ(0)}{dt}=0`` except for
 
 ```math
 \\frac{dx₆(0)}{dt} = 1.75