Fix "Similar code" issue in src/client/coding.js

[crcastle]

Similar code found in 1 other location (mass = 58)

https://codeclimate.com/github/crcastle/collaborative-code-conference/src/client/coding.js#issue_57036f53872f3300011356a6

for (var i = 0; i < languages.length; i++) {
  modeSelector.appendChild(languageListItem(languages[i].name, languages[i].mime));
}

and

for (var j = 0; j < themes.length; j++) {
  themeSelector.appendChild(themeListItem(themes[j].name, themes[j].classPrefix));
}