Dockerfile cache invalidating for nextepc build

support/docker/build/Dockerfile

@@ -7,14 +7,19 @@ MAINTAINER Sukchan Lee <acetcom@gmail.com>
 
 WORKDIR /tmp
 
-RUN	git clone https://github.com/acetcom/nextepc
+ARG USER=acetcom
+ARG REPO=nextepc
+ARG BRANCH=master
+RUN	git clone https://github.com/$USER/$REPO
+ADD https://api.github.com/repos/$USER/$REPO/git/refs/heads/$BRANCH /tmp/version.json
+
 RUN	cd nextepc && \
+	git fetch && git checkout -f -B master origin/master && \
     autoreconf -f -i && \
     ./configure \
         --prefix=/usr \
         --sysconfdir=/etc \
         --localstatedir=/var && \
-    make -j `nproc` && \
-    make install
+    make -j `nproc` install
 
 WORKDIR /root