feat(buster-slim-pg11): add gcc

This is needed for some pip packages such as pycrypto

library/buster-slim-pg11/Dockerfile

@@ -36,6 +36,7 @@
 	apt-utils \
 	nodejs \
 	git \
+	gcc \
 	sudo \
 	&& pg_dropcluster 11 main
 
@@ -50,4 +51,4 @@
 RUN useradd --create-home --user-group --shell /bin/bash user
 RUN echo "user   ALL=(ALL)       NOPASSWD:ALL" > /etc/sudoers.d/user
 USER user
-WORKDIR /home/user
+WORKDIR /home/user
\ No newline at end of file