Fix doctest for sphinx

Author: uvchik

windpowerlib/wind_turbine.py

@@ -237,11 +237,15 @@ def to_group(self, number_turbines=None, total_capacity=None):
         3.5
         >>> e126.to_group(total_capacity=12600000).wind_turbine.nominal_power
         4200000.0
-        >>> e126.to_group(5)
-        WindTurbineGroup(wind_turbine=Wind turbine: E-126/4200 ['nominal\
- power=4200000.0 W', 'hub height=135 m', 'rotor diameter=127.0 m',\
- 'power_coefficient_curve=True', 'power_curve=True'], number_of_turbines=5)
+        >>> type(e126.to_group(5))
+        <class 'windpowerlib.wind_turbine.WindTurbineGroup'>
+        >>> e126.to_group(5)  # doctest: +NORMALIZE_WHITESPACE
+        WindTurbineGroup(wind_turbine=Wind turbine: E-126/4200 ['nominal
+        power=4200000.0 W', 'hub height=135 m', 'rotor diameter=127.0 m',
+        'power_coefficient_curve=True', 'power_curve=True'],
+        number_of_turbines=5)
         """
+
         if number_turbines is not None and total_capacity is not None:
             raise ValueError("The 'number' and the 'total_capacity parameter "
                              "are mutually exclusive. Use just one of them.")