Replace "MENU" text in svg by path

After installing the theme, I noticed that the text "MENU" for the menu icon was cut off. It seems browsers don't render webfonts inside SVGs. On a system with Source Pro installed system wide, it looks as intended.
See http://www.browserstack.com/screenshots/67c19ed483d634c342de837dd6baa9602f6f07f7.

Therefore I replaced the text with its path (precision truncated to 2 decimals) which of course increases the base64-encoded size quite a bit ([see diff](https://github.com/omphalosskeptic/mnml-ghost-theme/pull/23/files?diff=split)) but enables correct rendering:

    - <text y='23' font-size='10px' fill='slategray' font-weight='400' font-family='Source Sans Pro'>MENU</text>
    + <path d="m1 23 0.77 0 0-3.61c0-0.58-0.07-1.36-0.11-1.94l0.04 0 0.52 1.46 1.27 3.43 0.47 0 1.26-3.43 0.53-1.46 0.04 0c-0.05 0.58-0.11 1.36-0.11 1.94l0 3.61 0.79 0 0-6.56-0.98 0-1.26 3.52-0.46 1.34-0.04 0L3.25 19.96 1.98 16.44 1 16.44 1 23M8.27 23l3.88 0 0-0.71-3.05 0 0-2.38 2.49 0 0-0.71-2.49 0 0-2.06 2.95 0 0-0.7-3.78 0 0 6.56M13.54 23l0.79 0 0-3.43c0-0.69-0.06-1.39-0.11-2.05l0.04 0 0.71 1.35 2.38 4.13 0.86 0 0-6.56-0.79 0 0 3.39c0 0.69 0.06 1.43 0.1 2.09l-0.04 0-0.71-1.36-2.37-4.12-0.86 0 0 6.56M19.97 20.29c0 2.11 1.02 2.83 2.36 2.83 1.34 0 2.35-0.72 2.35-2.83l0-3.85-0.8 0 0 3.87c0 1.58-0.68 2.08-1.55 2.08-0.86 0-1.53-0.5-1.53-2.08l0-3.87-0.83 0 0 3.85" fill="#708090"/>