perf: update default text-color

Author: tangjinzhou

components/style/themes/default.less

@@ -47,7 +47,7 @@
   'Microsoft YaHei', 'Helvetica Neue', Helvetica, Arial, sans-serif, 'Apple Color Emoji',
   'Segoe UI Emoji', 'Segoe UI Symbol';
 @code-family: 'SFMono-Regular', Consolas, 'Liberation Mono', Menlo, Courier, monospace;
-@text-color: fade(@black, 65%);
+@text-color: fade(@black, 85%);
 @text-color-secondary: fade(@black, 45%);
 @text-color-inverse: @white;
 @icon-color: inherit;