Remove redundant cd

Author: nerdcha

Dockerfile

@@ -111,6 +111,6 @@ RUN apt-get install -y python-software-properties && \
     cd /usr/local/src/mxnet && cp make/config.mk . && sed -i 's/CC = gcc/CC = gcc-4.8/' config.mk && \
     sed -i 's/CXX = g++/CXX = g++-4.8/' config.mk && \
     sed -i 's/ADD_LDFLAGS =/ADD_LDFLAGS = -lstdc++/' config.mk && \
-    cd mxnet && make && cd python && python setup.py install
+    make && cd python && python setup.py install