Update Dockerfile

Dockerfile

@@ -1,7 +1,7 @@
 FROM r-base:4.1.0
 MAINTAINER Disease Transcriptomics Lab <imm-nmorais@medicina.ulisboa.pt>
 
-RUN apt-get update && apt-get -y upgrade && apt-get -y autoremove
+RUN apt-get update && apt-get -y upgrade && apt-get -y autoremove && apt-get clean
 RUN apt-get install -y curl
 RUN apt-get install -y libcurl4-openssl-dev
 RUN apt-get install -y libssl-dev