Disable ligatures inside the editor

Closes #3899

lib/codemirror.css

@@ -245,6 +245,8 @@ div.CodeMirror span.CodeMirror-nonmatchingbracket {color: #f22;}
   position: relative;
   overflow: visible;
   -webkit-tap-highlight-color: transparent;
+  -webkit-font-variant-ligatures: none;
+  font-variant-ligatures: none;
 }
 .CodeMirror-wrap pre {
   word-wrap: break-word;