Removing quotes from @each arguments

Quoted arguments passed to `@each in` are not handled as you might expect in Sass. Instead, the values should be passed in without quotes.

Before
```scss
@each $align in ('left', 'right', 'center', 'justify') {
  .text-#{$align} {
    text-align: $align;
  }
}

// Output CSS Looks like this
.text-center {
  text-align: "center";
}
```

After
```scss
@each $align in (left, right, center, justify) {
  .text-#{$align} {
    text-align: $align;
  }
}

// Output CSS Looks like this
.text-center {
  text-align: center;
}
```

Let me know if you'd like to handle this some other way. I haven't tested against multiple versions of Sass, but I'm on `Sass 3.4.6`.