Issue title: HTTPS breaks hot reloading while proxied through browser-sync
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* Operating System: ubuntu
* Node Version: v7.6.0
* NPM Version: 4.1.2
* webpack Version: 2.2.1
* webpack-dev-server Version: 2.9.2

<!-- Please place an x, no spaces, in all [ ] that apply -->

- [x] This is a **bug**
- [ ] This is a **feature** request
- [ ] This is a **modification** request

### Code

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  short snippets below.

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```js
new BrowserSyncPlugin({
        host: 'localhost',
        port: 3333,
        https: {
          "key": "/home/erez/stuff/xsites/devops/ssl-cert/test.key.pem",
          "cert": "/home/erez/stuff/xsites/devops/ssl-cert/test.cert.pem",
        },
        proxy: 'https://localhost:3030/',
        scrollThrottle: 100
    }, {
        reload: false 
    })
```
### Expected Behavior
browser should reload on js changes, and inject changes on css changes.
### Actual Behavior
nothing happens
### For Bugs; How can we reproduce the behavior?
serving webpack-dev-server output through webpack's BrowserSyncPlugin plugin worked without issues when wasn't https. Once switched to https it gives:
`VM46:1 GET https://localhost:3030/sockjs-node/info?t=1508415256328 net38d1:d2b4:3d06:83e8:96a5:8c2:893d:aba5RR_INSECURE_RESPONSE`

Im running dev-server with:
`webpack-dev-server --https --client-log-level=error --port=3030 --inline --hot --content-base dist/`

### For Features; What is the motivation and/or use-case for the feature?


 Comments: 
 Comment 0: @NitsanBaleli because we know that this doesn't happen _without_ the `BrowserSyncPlugin`, I'm not convinced this is a bug with webpack-dev-server. Have you taken to StackOverflow and/or the webpack Gitter for support on this yet? I'd also suggest creating an issue at https://github.com/Va1/browser-sync-webpack-plugin as your third stop to triaging this issue. I'll lave this open for a bit in the event you find a cause within this module, but we see plugins and loaders screw up WDS all the time, not at the fault of WDS. 
 Comment 1: @NitsanBaleli please do follow up if this is still a pressing issue. If we reach 30 days without comment it'll be marked as abandoned/stale and closed.
{'source': 'GithubIssues', 'repo_name_with_owner': 'webpack/webpack-dev-server', 'issue_id': 266822382, 'repo_stars': 7879.0}