julia: fix mx.forward kwargs checking

[iblislin]

close dmlc/MXNet.jl#431

• test case included

[Vikas-kum]

@iblis17 the ci is failing on this PR. Please take a look at this - http://jenkins.mxnet-ci.amazon-ml.com/blue/organizations/jenkins/mxnet-validation%2Funix-gpu/detail/master/1034/pipeline

And make sure that, CI passes and there is at least one review(just another pair of eyes looking at changes)

[iblislin]

http://jenkins.mxnet-ci.amazon-ml.com/blue/organizations/jenkins/mxnet-validation%2Funix-gpu/detail/master/1034/pipeline

hmm, I don't think it's related to this PR.

And make sure that, CI passes

yeah, it passed
https://github.com/apache/incubator-mxnet/pull/16138/commits

and there is at least one review(just another pair of eyes looking at changes)

Okay, I will wait for someone review it next time.

[Vikas-kum]

No issues, thanks for checking. We will check if this is one off failure.
We are trying to make master stable, best effort. The CI test that runs on PR is just unit tests. There are several other test that runs when PR gets merged into master. So, CI can find regressions after getting merged into master and there we would require help from PR writers to investigate failures.