Toolbar buttons don't have focus styles

[ralrom]

Buttons in the toolbar have no visual indication that they are focused when going through them via the tab key.

They have the button:hover but are missing the button:focus selector in base.styl:

  button:hover, button.ql-active,
  .ql-picker-label:hover, .ql-picker-label.ql-active,
  .ql-picker-item:hover, .ql-picker-item.ql-selected
    color: activeColor
    .ql-fill, .ql-stroke.ql-fill
      fill: activeColor
    .ql-stroke, .ql-stroke-miter
      stroke: activeColor

Steps for Reproduction

1. Visit https://quilljs.com/standalone/snow
2. Tab several times

Expected behavior:

The active toolbar button is blue

Actual behavior:

The active toolbar button remains black

Platforms:

Chrome 58 on macOs 10.12

Version:

1.2.6