docs: fix Mixins Reference

Author: thingsym

docs/index.html

@@ -736,7 +736,7 @@ <h3 class="reference"><span class="small">@include</span> <span class="big">grid
     <td>$col</td>
     <td>null</td>
     <td>null | initial | &lt;<a href="http://www.w3.org/TR/CSS21/syndata.html#numbers" target="_blank">number</a>&gt; | auto | equal | none | positive | &lt;<a href="http://www.w3.org/TR/CSS21/visudet.html#the-width-property" target="_blank">width</a>&gt;</td>
-    <td>define columns. <code>null</code> is no set columns. <code>&lt;number&gt;</code> is number of columns. <code>initial</code>, <code>auto</code>, <code>equal</code>, <code>none</code>, <code>positive</code> are preset columns. <code>&lt;width&gt;</code> is unit set columns (<code>&lt;width&gt;</code> is experimental stage. <code>&lt;breakpoint&gt;</code> is deprecated, use <code>&lt;initial&gt;</code> instead).</td>
+    <td>define columns. <code>null</code> is no set columns. <code>&lt;number&gt;</code> is number of columns. <code>initial</code>, <code>auto</code>, <code>equal</code>, <code>none</code>, <code>positive</code> are preset columns (Keyword values). <code>equal</code> as flex: 1. <code>&lt;width&gt;</code> is unit set columns (<code>&lt;width&gt;</code> is experimental stage. <code>&lt;breakpoint&gt;</code> is deprecated, use <code>&lt;initial&gt;</code> instead).</td>
     <td class="example"><a href="example-dart-sass/example.html#preset-grid-columns"><i class="fas fa-external-link-alt"></i></a></td>
     </tr>
     <tr>