Update Dockerfile.gpu

small fix taken from here floydhub#50

Dockerfile.gpu

@@ -224,7 +224,7 @@ RUN git clone --depth 1 https://github.com/opencv/opencv.git /root/opencv && \
 	cd /root/opencv && \
 	mkdir build && \
 	cd build && \
-	cmake -DWITH_QT=ON -DWITH_OPENGL=ON -DFORCE_VTK=ON -DWITH_TBB=ON -DWITH_GDAL=ON -DWITH_XINE=ON -DBUILD_EXAMPLES=ON .. && \
+	cmake -DCMAKE_LIBRARY_PATH=/usr/local/cuda/lib64/stubs -DWITH_QT=ON -DWITH_OPENGL=ON -DFORCE_VTK=ON -DWITH_TBB=ON -DWITH_GDAL=ON -DWITH_XINE=ON -DBUILD_EXAMPLES=ON .. && \
 	make -j"$(nproc)"  && \
 	make install && \
 	ldconfig && \