clear apt cache to optimize verilog dockerfile

Author: GREENRAT-K405

Dockerfile.v

@@ -1,7 +1,7 @@
 FROM ubuntu:20.04
 
 RUN apt-get update && DEBIAN_FRONTEND=noninteractive apt-get install -y --no-install-recommends \
-        iverilog
+        iverilog && rm -rf /var/lib/apt/lists/*
 
 COPY . /src
 WORKDIR /src