Fix apt cache cleanup path in Dockerfile example

19_observability/19.3_performance_optimization.md

@@ -510,7 +510,7 @@ WORKDIR /build
 
 RUN apt-get update && apt-get install -y --no-install-recommends \
     build-essential \
-    && rm -rf /var/apt/lists/*
+    && rm -rf /var/lib/apt/lists/*
 
 COPY requirements.txt .
 RUN pip install --user --no-cache-dir -r requirements.txt