Removed extraneous font-family mentions of Ubuntu Mono.

I used the following code to ensure that the rules I excised
font-family declarations from still inherited Ubuntu Mono from
parent nodes:

(function(jQuery) {
  var $ = jQuery;

  function test(name, selectors, css) {
    console.log("CSS test: " + name);
    selectors.forEach(function(selector) {
      var passed = 0;
      var elements = $(selector);
      if (!elements.length)
        return console.error("  FAIL - nothing matches " + selector);
      elements.each(function() {
        var $el = $(this);
        for (var property in css) {
          var value = $el.css(property);
          if (!value.match(css[property]))
            return console.error("  FAIL - " + selector + " " + property +
                                 " is " + value + ", not " + css[property]);
        }
        passed++;
      });
      if (elements.length == passed)
        console.log("  OK    - " + selector + " (" + passed + ")");
    });
  }

  test("font is Ubuntu Mono", [
    ".CodeMirror", ".CodeMirror-lines", ".CodeMirror textarea",
    ".CodeMirror-gutter-text", ".cm-s-jsbin span.cm-comment"
  ], {
    'font-family': /Ubuntu Mono/
  });
})(jQuery);

css/jsbin-codemirror-theme.css

@@ -25,7 +25,6 @@
 }
 
 .CodeMirror .CodeMirror-lines {
-  font-family: 'Ubuntu Mono', monospace;
   color: #333;
   font-size: 14px;
   line-height: 15.75px;
@@ -43,7 +42,6 @@
 }
 
 .CodeMirror-gutter-text {
-  font-family: 'Ubuntu Mono', monospace;
   color: #A9A9A9;
   font-size: 12px;
   line-height: 15.75px;
@@ -54,11 +52,13 @@
 }
 
 .cm-s-jsbin span.cm-comment {
-  font-family: 'Ubuntu Mono', monospace;
   color: #333;
   font-style: italic;
   font-weight: bold;
-  line-height: 15.75px; /* needs to be a little less than the standard line-height to align on multi-line wrapped content */
+
+  /* This needs to be a little less than the standard line-height to align on
+     multi-line wrapped content. */
+  line-height: 15.75px;
 }
 
 .CodeMirror-wrap .CodeMirror-scroll {