use apt-get instead of apt

according to some tool inside my editor apt is a user facing tool and it is recommended to use apt-get instead

Dockerfile

@@ -6,7 +6,7 @@ COPY requirements.txt .
 
 RUN python3 -m pip install -r requirements.txt
 
-RUN apt update && apt install -y imagemagick ffmpeg libsm6 libxext6 graphviz
+RUN apt-get update && apt-get install -y imagemagick ffmpeg libsm6 libxext6 graphviz
 
 COPY . .