add libxslt (required)

Dockerfile

@@ -4,7 +4,7 @@ LABEL maintainer="Julien Cabillot <dockerimages@cabillot.eu>"
 ENV NOKOGIRI_USE_SYSTEM_LIBRARIES=1
 
 RUN apk --no-cache upgrade && \
-    apk --no-cache add ruby && \
+    apk --no-cache add ruby libxslt && \
     apk --no-cache add --virtual build-dependencies \
         build-base \
         libxml2-dev \