Add emsdk_env when building docker image.
diff --git a/docker/Dockerfile b/docker/Dockerfile
index f58c5ce..354fd37 100644
--- a/docker/Dockerfile
+++ b/docker/Dockerfile
@@ -35,6 +35,7 @@
&& ./emsdk activate ${EMSCRIPTEN_VERSION} \
&& chmod 777 ${EMSDK}/upstream/emscripten \
&& chmod -R 777 ${EMSDK}/upstream/emscripten/cache \
+ && . ./emsdk_env.sh \
&& echo "int main() { return 0; }" > hello.c \
&& ${EMSDK}/upstream/emscripten/emcc -c hello.c \
&& cat ${EMSDK}/upstream/emscripten/cache/sanity.txt \