use opt instead of tmp as install dir

Dockerfile

@@ -13,8 +13,8 @@ ENV LC_ALL en_US.UTF-8
 ENV LANG en_US.UTF-8
 ENV LANGUAGE en_US.UTF-8
 
-RUN wget -q https://github.com/ossrs/srs/archive/v2.0-r2.zip -P /tmp/ && \
-	cd /tmp && \
+RUN wget -q https://github.com/ossrs/srs/archive/v2.0-r2.zip -P /opt/ && \
+	cd /opt && \
 	unzip v2.0-r2.zip && \
 	rm -f v2.0-r2.zip
 
@@ -24,7 +24,7 @@ EXPOSE 8080
 # for nginx gzip module
 RUN apt-get install zlib1g-dev
 
-RUN cd /tmp/srs-2.0-r2/trunk && \
+RUN cd /opt/srs-2.0-r2/trunk && \
 	./configure --with-hls --with-dvr --with-nginx --with-transcode --with-ingest --with-stat --with-http-callback --with-http-server --with-http-api --log-trace \
 				--without-hds --without-ssl --without-ffmpeg --without-stream-caster --without-librtmp --without-research --without-utest --without-gperf --without-gmc --without-gmp --without-gcp --without-gprof --without-arm-ubuntu12 --without-mips-ubuntu12	\
 				--jobs=4 --x86-x64 --log-trace && \