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