chore: update code style (flake8)

Author: chilango74

okama/__init__.py

@@ -44,4 +44,5 @@ def __getattr__(name):
         return okama.api.namespaces.get_macro_namespaces()
     raise AttributeError(f"module '{__name__}' has no attribute '{name}'")
 
+
 __version__ = version("okama")

okama/frontier/single_period.py

@@ -927,7 +927,8 @@ def plot_transition_map(self, x_axe: str = 'risk', figsize: Optional[tuple] = No
         >>> x.plot_transition_map()
         >>> plt.show()
 
-        Transition Map with default setting show the relation between Risk (stanrd deviation) and assets weights for optimized portfolios.
+        Transition Map with default setting show the relation between Risk (stanrd deviation) and assets weights for
+        optimized portfolios.
         The same relation for CAGR can be shown setting x_axe='cagr'.
 
         >>> x.plot_transition_map(x_axe='cagr')