Increase the usage of augmented assignment statements

[elfring]

👀 Some source code analysis tools can help to find opportunities for improving software components.
💭 I propose to increase the usage of augmented assignment statements accordingly.

diff --git a/Python/LeniaND.py b/Python/LeniaND.py
index 1c05acc..892d0f0 100644
--- a/Python/LeniaND.py
+++ b/Python/LeniaND.py
@@ -676,7 +676,7 @@ class Analyzer:
 
                 self.density_sum = np.sum(self.polar_density, axis=0)
                 if self.density_ema is not None:
-                    self.density_ema = self.density_ema + self.ema_alpha * (self.density_sum - self.density_ema)
+                    self.density_ema += self.ema_alpha * (self.density_sum - self.density_ema)
                 else:
                     self.density_ema = self.density_sum
 
diff --git a/Python/LeniaNDK.py b/Python/LeniaNDK.py
index 03373fe..8722d87 100644
--- a/Python/LeniaNDK.py
+++ b/Python/LeniaNDK.py
@@ -701,7 +701,7 @@ class Analyzer:
 
                 self.density_sum = np.sum(self.polar_density, axis=0)
                 if self.density_ema is not None:
-                    self.density_ema = self.density_ema + self.ema_alpha * (self.density_sum - self.density_ema)
+                    self.density_ema += self.ema_alpha * (self.density_sum - self.density_ema)
                 else:
                     self.density_ema = self.density_sum
 
diff --git a/Python/LeniaNDKC.py b/Python/LeniaNDKC.py
index 765e00f..038e096 100644
--- a/Python/LeniaNDKC.py
+++ b/Python/LeniaNDKC.py
@@ -751,7 +751,7 @@ class Analyzer:
 
                 self.density_sum = np.sum(self.polar_density, axis=0)
                 if self.density_ema is not None:
-                    self.density_ema = self.density_ema + self.ema_alpha * (self.density_sum - self.density_ema)
+                    self.density_ema += self.ema_alpha * (self.density_sum - self.density_ema)
                 else:
                     self.density_ema = self.density_sum