Update docs-example base image (#104)

That commit also will be fix CVE-2022-48541

Dockerfile

@@ -204,7 +204,7 @@ RUN mkdir -p \
 USER ds
 ENTRYPOINT docker-entrypoint.sh /var/www/$COMPANY_NAME/documentserver/server/FileConverter/converter
 
-FROM node:buster AS example
+FROM node:lts-buster-slim AS example
 LABEL maintainer Ascensio System SIA <[email protected]>
 
 ENV LANG=en_US.UTF-8 \
@@ -215,7 +215,9 @@ ENV LANG=en_US.UTF-8 \
 
 WORKDIR /var/www/onlyoffice/documentserver-example/
 
-RUN git clone \
+RUN apt update -y && \
+    apt install git -y && \
+    git clone \
       --depth 1 \
       --recurse-submodules \
       https://github.com/ONLYOFFICE/document-server-integration.git && \