Improve formatting of episode 16 solution

Simulating a dynamical system solution had a new line in the code block which caused the whole block not to be rendered.

episodes/16-writing-functions.md

@@ -573,21 +573,25 @@ density. In the model, time takes discrete values 0, 1, 2, ...
 
 ## Solution
 
-1. ```python
+1.
+  ```python
   def logistic_map(x, r):
       return r * x * (1 - x)
   ```
 
-2. ```python
+2.
+  ```python
   initial_population = 0.5
   t_final = 10
   r = 1.0
   population = [initial_population]
+
   for t in range(t_final):
       population.append( logistic_map(population[t], r) )
   ```
 
-3. ```python
+3.
+  ```python
   def iterate(initial_population, t_final, r):
       population = [initial_population]
       for t in range(t_final):
@@ -598,7 +602,7 @@ density. In the model, time takes discrete values 0, 1, 2, ...
       population = iterate(0.5, period, 1)
       print(population[-1])
   ```
-  
+
   ```output
   0.06945089389714401
   0.009395779870614648