Use `textContent` when `innerText` is not available.

Firefox does not implement `innerText` so this led to another `TypeError`.
fixing prop order on android theme
fixing prop order on ios theme
Re-enable clean-css's advanced optimizations.

The issue was fixed in v2.1.8.
Merge pull request #518 from twbs/innerText

Use `textContent` when `innerText` is not available.
Update "grunt-contib-concat" dependency.
Grunt.
fixing prop order in the lib scss
updating the docs order
Merge pull request #522 from twbs/clean-css-skip-advanced

Re-enable clean-css's advanced optimizations.
Merge pull request #534 from twbs/prop-order

Property order
Add Autoprefixer support.
Refactor properties.
Refactor Gruntfile.js targets.
Run `grunt`.