Add http(s) proxy support

[wangshijun]

My users donot have direct network access to api.ai, but the proxy feature is missing from current version, so I implemented proxy feature with the awesome proxy-agent lib.

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[wangshijun]

I signed it!

[googlebot]

CLAs look good, thanks!

[rjivan]

I'm looking for the same feature. Is there anything that's preventing this from being merged?

[wangshijun]

@rjivan you can just use my branch by yarn add wangshijun@apiai-nodejs-client

[sctse999]

Hello, can anyone pls merge this PR? this is quite needed

[lmonzon]

@wangshijun no work yarn add wangshijun@apiai-nodejs-client

[sctse999]

@sstepashka could you pls take a look at this PR and merge if possible? Really want to work with the official library instead of a forked one.....

[supradeepk]

please add this

[ChellaTheCoder]

Is it merged or any alternative for proxy support ?