Add super().__init__() to Mesa model initalization (#175)

When inheriting from a Mesa Model you always need to initialize it by calling super().__init__(). This commit fixes that in two gis models.

gis/geo_schelling/model.py

@@ -52,6 +52,7 @@ class GeoSchelling(mesa.Model):
     """Model class for the Schelling segregation model."""
 
     def __init__(self, density=0.6, minority_pc=0.2, export_data=False):
+        super().__init__()
         self.density = density
         self.minority_pc = minority_pc
         self.export_data = export_data

gis/geo_sir/model.py

@@ -24,6 +24,7 @@ def __init__(
         :param infection_risk:      Probability of agent to become infected,
                                     if it has been exposed to another infected
         """
+        super().__init__()
         self.schedule = mesa.time.BaseScheduler(self)
         self.space = mg.GeoSpace(warn_crs_conversion=False)
         self.steps = 0