Adjust suggested "dpkg" usage to account for potentially receiving an arch tuple

Fixes #24; thanks @dol!

Author: tianon

README.md

@@ -28,8 +28,9 @@ We assume installation inside Docker (probably not the right tool for most use-c
 ENV GOSU_VERSION 1.9
 RUN set -x \
 	&& apt-get update && apt-get install -y --no-install-recommends ca-certificates wget && rm -rf /var/lib/apt/lists/* \
-	&& wget -O /usr/local/bin/gosu "https://github.com/tianon/gosu/releases/download/$GOSU_VERSION/gosu-$(dpkg --print-architecture)" \
-	&& wget -O /usr/local/bin/gosu.asc "https://github.com/tianon/gosu/releases/download/$GOSU_VERSION/gosu-$(dpkg --print-architecture).asc" \
+	&& dpkgArch="$(dpkg --print-architecture | awk -F- '{ print $NF }')" \
+	&& wget -O /usr/local/bin/gosu "https://github.com/tianon/gosu/releases/download/$GOSU_VERSION/gosu-$dpkgArch" \
+	&& wget -O /usr/local/bin/gosu.asc "https://github.com/tianon/gosu/releases/download/$GOSU_VERSION/gosu-$dpkgArch.asc" \
 	&& export GNUPGHOME="$(mktemp -d)" \
 	&& gpg --keyserver ha.pool.sks-keyservers.net --recv-keys B42F6819007F00F88E364FD4036A9C25BF357DD4 \
 	&& gpg --batch --verify /usr/local/bin/gosu.asc /usr/local/bin/gosu \
@@ -48,8 +49,9 @@ RUN set -x \
 		dpkg \
 		gnupg \
 		openssl \
-	&& wget -O /usr/local/bin/gosu "https://github.com/tianon/gosu/releases/download/$GOSU_VERSION/gosu-$(dpkg --print-architecture)" \
-	&& wget -O /usr/local/bin/gosu.asc "https://github.com/tianon/gosu/releases/download/$GOSU_VERSION/gosu-$(dpkg --print-architecture).asc" \
+	&& dpkgArch="$(dpkg --print-architecture | awk -F- '{ print $NF }')" \
+	&& wget -O /usr/local/bin/gosu "https://github.com/tianon/gosu/releases/download/$GOSU_VERSION/gosu-$dpkgArch" \
+	&& wget -O /usr/local/bin/gosu.asc "https://github.com/tianon/gosu/releases/download/$GOSU_VERSION/gosu-$dpkgArch.asc" \
 	&& export GNUPGHOME="$(mktemp -d)" \
 	&& gpg --keyserver ha.pool.sks-keyservers.net --recv-keys B42F6819007F00F88E364FD4036A9C25BF357DD4 \
 	&& gpg --batch --verify /usr/local/bin/gosu.asc /usr/local/bin/gosu \