Support current version of mxnet

[leezu]

It seems mxnet.js does not compile with current versions of mxnet.

Can you give some suggestions where to pick up the work to bring mxnet.js up to date with the current mxnet? Will the compatibility be affected by the (as far as I understand soonish) merge of nnvm?

[leezu]

The error lies within the amalgamation code. This has been fixed with apache/mxnet#4135 and I have confirmed that the mxnet.js image classification demo works with a recompiled version of libmxnet_predict.js (based on apache/mxnet@c05efbe ).

I noticed that the compilation will only work with a recent version of emscripten (at least it fails for me with the distro provided version of Ubuntu 16.04).

Would you be willing to accept a pull request that updates mxnet to above mentioned commit and adds a notice about the emscripten version?