fix: use UI-font for markdown body strings

Author: aviatesk

styles/atom-ide-datatips-marked.less

@@ -7,8 +7,8 @@
 
 .datatip-marked-container {
   color: @syntax-text-color;
-  font-family: var(--editor-font-family);
-  font-size: var(--editor-font-size);
+  font-family: @font-family;
+  font-size: @font-size;
   max-height: 400px;
   max-width: 64em;
   overflow: auto;