enable variable override

.s2i/bin/assemble

@@ -3,9 +3,9 @@
 # Exit on any error
 set -e
 
-hugo_version=0.54.0
-hugo_bin_name=hugo_${hugo_version}_Linux-64bit.tar.gz
-hugo_bin_url=https://github.com/gohugoio/hugo/releases/download/v${hugo_version}/${hugo_bin_name}
+hugo_version=${HUGO_VERSION:-0.54.0}
+hugo_bin_name=${HUGO_BIN_NAME:-hugo_${hugo_version}_Linux-64bit.tar.gz}
+hugo_bin_url=${HUGO_BIN_URL:-https://github.com/gohugoio/hugo/releases/download/v${hugo_version}/${hugo_bin_name}}
 
 # Download Hugo
 curl -s -o "/tmp/${hugo_bin_name}" -L  "${hugo_bin_url}"