Fix .social-share-button-qq background image position

@media only screen and (-webkit-device-pixel-ratio: 2) {
...
.social-share-button-qq
...
}
Merge pull request #27 from miclle/patch-1

Fix .social-share-button-qq background image position
Merge branch 'master' of https://github.com/huacnlee/social-share-button
Pinterest.