Support alpine more completely in the helper scripts

Author: tianon

generate-stackbrew-library.sh

@@ -31,6 +31,7 @@ for version in "${versions[@]}"; do
 	done
 
 	for variant in onbuild slim alpine; do
+		[ -d "$version/$variant" ] || continue
 		commit="$(cd "$version/$variant" && git log -1 --format='format:%H' -- Dockerfile $(awk 'toupper($1) == "COPY" { for (i = 2; i < NF; i++) { print $i } }' Dockerfile))"
 		echo
 		for va in "${versionAliases[@]}"; do

update.sh

@@ -32,7 +32,7 @@ for version in "${versions[@]}"; do
 			s/^(ENV RUBY_DOWNLOAD_SHA256) .*/\1 '"$shaVal"'/;
 			s/^(ENV BUNDLER_VERSION) .*/\1 '"$bundler"'/;
 			s/^(ENV RUBYGEMS_VERSION) .*/\1 '"$rubygems"'/;
-		' "$version/"{,slim/}Dockerfile
+		' "$version"{/,/*/}Dockerfile
 		sed -ri 's/^(FROM ruby):.*/\1:'"$version"'/' "$version/"*"/Dockerfile"
 	)
 done