Change ubuntu version and add dependencies.

Author: NlightNFotis

Dockerfile

@@ -1,5 +1,7 @@
-FROM ubuntu:21.04
+FROM ubuntu:20.04
 
-COPY /build/bin/* /home/cbmc/
+COPY /build-release/bin/* /home/cbmc/
+
+RUN apt-get update && apt-get install -y gcc
 
 CMD /bin/bash