Fix css plugin for IE7

`var style = document.createElement('style');`
`var useCssText = (style.styleSheet) ? true : false;`
`style.type = 'text/css';`

results in useCssText = false in IE7 which is causing wrong logic to execute for attaching css styles.

`var style = document.createElement('style');`
`style.type = 'text/css';`
`var useCssText = (style.styleSheet) ? true : false;`

results in useCssText = true, hence moving up style.type assignment.

IE7 also throws 'Access denied' exception on 

`style.styleSheet.cssText = [style.styleSheet.cssText, text].join('\n');`

It can not read value of the `style.styleSheet.cssText`, so replacing it with `style.innerHTML`.

I've checked value of `style.innerHTML` before and after adding styles using `style.styleSheet.cssText`. InnerHTML correctly reflects changes made via cssText so I think it should be a safe change.