Fix warnings

Author: devlights

.devcontainer/Dockerfile

@@ -8,8 +8,10 @@ RUN if [ "${NODE_VERSION}" != "none" ]; then su vscode -c "umask 0002 && . /usr/
 
 # [Optional] Uncomment this section to install additional OS packages.
 RUN apt-get update -q && export DEBIAN_FRONTEND=noninteractive \
-    && apt-get -yq install --no-install-recommends bash-completion
-RUN su vscode -c "source /etc/bash_completion"
+    && apt-get -yq install --no-install-recommends bash-completion \
+    && apt-get clean \
+    && rm -rf /var/lib/apt/lists/* \
+    && su vscode -c "source /etc/bash_completion"
 
 # [Optional] Uncomment this line to install global node packages.
 # RUN su vscode -c "source /usr/local/share/nvm/nvm.sh && npm install -g <your-package-here>" 2>&1