Fix verification no system-ruby deps installed

Author: Phileas Lebada

Dockerfile-alpine.template

@@ -114,10 +114,10 @@ RUN apk add --no-cache --virtual .ruby-builddeps \
 	gem update --system "$RUBYGEMS_VERSION"; \
 	rm -fr /root/.gem/; \
 # verify we have no "ruby" packages installed
-	! apk --no-network list --installed \
+	if apk --no-network list --installed \
 		| grep -v '^[.]ruby-rundeps' \
 		| grep -i ruby \
-	; \
+	; then false; fi; \
 	[ "$(command -v ruby)" = '/usr/local/bin/ruby' ]; \
 # rough smoke test
 	ruby --version; \

Dockerfile-debian.template

@@ -75,7 +75,7 @@ RUN savedAptMark="$(apt-mark showmanual)"; \
 	gem update --system "$RUBYGEMS_VERSION"; \
 	rm -fr /root/.gem/; \
 # verify we have no "ruby" packages installed
-	! dpkg -l | grep -i ruby; \
+	if dpkg -l | grep -i 'ruby'; then false; fi; \
 	[ "$(command -v ruby)" = '/usr/local/bin/ruby' ]; \
 # rough smoke test
 	ruby --version; \

Dockerfile-slim.template

@@ -100,7 +100,7 @@ RUN savedAptMark="$(apt-mark showmanual)"; \
 	gem update --system "$RUBYGEMS_VERSION"; \
 	rm -r /root/.gem/; \
 # verify we have no "ruby" packages installed
-	! dpkg -l | grep -i ruby; \
+	if dpkg -l | grep -i 'ruby'; then false; fi; \
 	[ "$(command -v ruby)" = '/usr/local/bin/ruby' ]; \
 # rough smoke test
 	ruby --version; \