Update SBCL version to 2.5.11 in Dockerfile

Author: stylewarning

sbcl/Dockerfile

@@ -4,7 +4,7 @@ LABEL org.opencontainers.image.source=https://github.com/coalton-lang/base-image
 LABEL org.opencontainers.image.description="SBCL base image for Coalton CI"
 LABEL org.opencontainers.image.licenses=MIT
 
-ARG SBCL_VERSION=2.5.8
+ARG SBCL_VERSION=2.5.11
 ARG SBCL_ARCH=x86-64
 
 # Install dependencies