BackstopJS compare process killed in Red Hat when there are 30+ scenarios to run

As the image show above, i have 30+ scenarios run in my Backstopjs task, the Casperjs script all run successfully, but when go in to compare section, it only successfully run several task, and then stop in showing **Killed** , I don't know what happened.

I guess there maybe some reason about the memory issue mention here: https://github.com/garris/BackstopJS/issues/462, and i set `"asyncCompareLimit": 100` in my backstop config, but the problem doesn't solved.

Then i tried to reduce my scenarios to run (from 30+ to 10), the problem didn't show, everything works fine.

I also tried run this task in my Macbook(with 30+ scenarios), it also works well.

My backstop config like below:

```
{
"id": "prod_test",
"viewports": [{
"name": "iphone6",
"width": 375,
"height": 667
}],
"scenarios": [{
"label": "default",
"url": "http://localhost:2012/online_test/?template=default",
"hideSelectors": [],
"removeSelectors": [],
"selectors": [
"document"
],
"readyEvent": null,
"delay": 1000,
"misMatchThreshold": 0.1,
"onBeforeScript": "onBefore.js",
"onReadyScript": "onReady.js"
}, {
"label": "springday",
"url": "http://localhost:2012/online_test/?template=springday",
"hideSelectors": [],
"removeSelectors": [],
"selectors": [
"document"
],
"readyEvent": null,
"delay": 1000,
"misMatchThreshold": 0.1,
"onBeforeScript": "onBefore.js",
"onReadyScript": "onReady.js"
}, {
"label": "darkgold",
"url": "http://localhost:2012/online_test/?template=darkgold",
"hideSelectors": [],
"removeSelectors": [],
"selectors": [
"document"
],
"readyEvent": null,
"delay": 1000,
"misMatchThreshold": 0.1,
"onBeforeScript": "onBefore.js",
"onReadyScript": "onReady.js"
}, {
"label": "lightflower",
"url": "http://localhost:2012/online_test/?template=lightflower",
"hideSelectors": [],
"removeSelectors": [],
"selectors": [
"document"
],
"readyEvent": null,
"delay": 1000,
"misMatchThreshold": 0.1,
"onBeforeScript": "onBefore.js",
"onReadyScript": "onReady.js"
}
// there are many scenarios like above, just with different url parameter
],
"paths": {
"bitmaps_reference": "backstop_data/bitmaps_reference",
"bitmaps_test": "backstop_data/bitmaps_test",
"casper_scripts": "backstop_data/casper_scripts",
"html_report": "backstop_data/html_report",
"ci_report": "backstop_data/ci_report"
},
"casperFlags": [],
"engine": "phantomjs",
"report": ["browser"],
"debug": false
}

```
I checked the files in /backstop_data/bitmaps_test, all scenarios generate file successfully, only the html report doesn't generate successfully.

Does anyone have any idea about my issue?