Change to use naoru v3.1.5.

Change Dockerfile to compile gem well without increasing docker image size.
Increment version of narou-alpine to v1.4

Dockerfile

@@ -1,7 +1,7 @@
 FROM openjdk:8-jre-alpine
 ENV AOZORA_EPUB3 AozoraEpub3-1.1.0b46.zip
 ENV KINDLEGEN kindlegen_linux_2.6_i386_v2_9.tar.gz
-ENV NAROU_VERSION 3.1.2
+ENV NAROU_VERSION 3.1.5
 WORKDIR /opt/narou
 
 RUN apk --update add ruby ruby-io-console ruby-json wget unzip && rm -rf /var/cache/apk/*
@@ -14,7 +14,9 @@ RUN wget http://kindlegen.s3.amazonaws.com/${KINDLEGEN} && \
     tar zxf ${KINDLEGEN} -C /opt/kindlegen && \
     rm ${KINDLEGEN}
 
-RUN gem install narou -v ${NAROU_VERSION} --no-document
+RUN apk add --no-cache --virtual .ruby-builddeps build-base libffi-dev ruby-dev && \
+    gem install narou -v ${NAROU_VERSION} --no-document && \
+    apk del .ruby-builddeps
 
 COPY init.sh /usr/local/bin
 

Makefile

@@ -1,11 +1,13 @@
 
+VERSION = v1.4
+
 OPTIONS = \
 	--build-arg http_proxy=${http_proxy} \
 	--build-arg https_proxy=${https_proxy} \
 	--build-arg ftp_proxy=${ftp_proxy} \
 	--build-arg no_proxy=${no_proxy}
 
 build: FORCE
-	docker build -t jam7/narou-alpine ${OPTIONS} .
+	docker build -t jam7/narou-alpine:${VERSION} ${OPTIONS} .
 
 FORCE: