Update Dockerfile

Dockerfile

@@ -131,7 +131,7 @@ RUN git clone https://github.com/stevenlovegrove/Pangolin.git && \
           -DCMAKE_DISABLE_FIND_PACKAGE_OpenEXR=ON \
 #          -DBUILD_EXAMPLES=OFF -DBUILD_TOOLS=OFF \
           .. && \
-    make -j1 && \
+    make -j2 && \
     make install && \
     ldconfig