If I set the style on any text in a `BrowserWindow` as such:

```
P {
   font-family: cursive;
}
```

...I would expect that text to take on a "cursive" look, much as it does when I apply the same style to a page loaded in Chrome Browser.

However in Electron 1.4.12 on Mac it looks like it's `serif`.

`cursive` is one of the W3C's five standard styles along with `serif`, `sans-serif`, `monospace`, and `fantasy` [1]. All of these work as expected in Electron except `cursive`.

It seems it should work just like the others. I presume it's just an omission somewhere?

Thanks!

[1] https://www.w3.org/wiki/CSS/Properties/font-family
atom/browser/web_contents_preferences.cc
if (IsSandboxed(web_contents))
    command_line->AppendSwitch(switches::kEnableSandbox);
  
  base::FilePath::StringType preload;
  if (web_preferences.GetString(options::kPreloadScript, &preload)) {
    if (base::FilePath(preload).IsAbsolute())
      command_line->AppendSwitchNative(switches::kPreloadScript, preload);
    else
      LOG(ERROR) << "preload script must have absolute path.";
  } else if (web_preferences.GetString(options::kPreloadURL, &preload)) {
    
    base::FilePath preload_path;
    if (net::FileURLToFilePath(GURL(preload), &preload_path))
      command_line->AppendSwitchPath(switches::kPreloadScript, preload_path);
    else
      LOG(ERROR) << "preload url must be file:// protocol.";
  }
  
  std::string color;
  if (web_preferences.GetString(options::kBackgroundColor, &color))
    command_line->AppendSwitchASCII(switches::kBackgroundColor, color);
  
  double zoom_factor = 1.0;
  if (web_preferences.GetDouble(options::kZoomFactor, &zoom_factor) &&
      zoom_factor != 1.0)
    command_line->AppendSwitchASCII(switches::kZoomFactor,
                                    base::DoubleToString(zoom_factor));