Add git-lfs package to emsdk Docker image (#665)

Having LFS support already in the image saves some build time and allows a more consistent experience to other CI build images.

docker/Dockerfile

@@ -101,6 +101,7 @@ RUN echo "## Update and install packages" \
         zip \
         unzip \
         git \
+        git-lfs \
         ssh-client \
         build-essential \
         make \