refactor:优化样式

static/css/markdown.preview.css

@@ -175,4 +175,7 @@
 }
 .editormd-preview-container ol.linenums>li:last-child ,.editormd-html-preview ol.linenums>li:last-child{
     padding-bottom: 10px;
+}
+.editormd-preview-container ul>li{
+    line-height: 2em;
 }