Specify font-family for identicon in notification

Fixes #904, where letters in notification bubbles were being
displayed in serif font on Antergos (Arch) OS.

// FREEBIE

background.html

@@ -216,7 +216,7 @@
   <script type='text/x-tmpl-mustache' id='identicon-svg'>
       <svg xmlns='http://www.w3.org/2000/svg' width='100' height='100'>
          <circle cx='50' cy='50' r='40' fill='{{ color }}' />
-          <text text-anchor='middle' fill='white' font-size='24px' x='50' y='50' baseline-shift='-8px'>
+          <text text-anchor='middle' fill='white' font-family='sans-serif' font-size='24px' x='50' y='50' baseline-shift='-8px'>
               {{ content }}
           </text>
       </svg>

test/index.html

@@ -200,7 +200,7 @@
   <script type='text/x-tmpl-mustache' id='identicon-svg'>
       <svg xmlns='http://www.w3.org/2000/svg' width='100' height='100'>
          <circle cx='50' cy='50' r='40' fill='{{ color }}' />
-          <text text-anchor='middle' fill='white' font-size='24px' x='50' y='50' baseline-shift='-8px'>
+          <text text-anchor='middle' fill='white' font-family='sans-serif' font-size='24px' x='50' y='50' baseline-shift='-8px'>
               {{ content }}
           </text>
       </svg>