Update .gitpod.Dockerfile

clean up the local cache of package lists

Author: StarTrooper08

.gitpod.Dockerfile

@@ -23,7 +23,8 @@ RUN sed -i.bak "/^#.*deb-src.*universe$/s/^# //g" /etc/apt/sources.list \
     && apt -y build-dep r-base-dev \
     && apt -y install r-base-dev \
     && Rscript -e "install.packages('languageserver', repos='https://cran.rstudio.com')" \
-    && Rscript -e "install.packages('httpgd', repos='https://cran.rstudio.com')"
+    && Rscript -e "install.packages('httpgd', repos='https://cran.rstudio.com')" \
+    && rm -rf /var/lib/apt/lists/*
 
 RUN apt install -y shellcheck
 RUN apt install -y ccache