docs: update examples

Author: mrholek

packages/docs/content/components/placeholder.mdx

@@ -55,7 +55,7 @@ In the example below, we take a typical card component and recreate it with plac
       <CPlaceholder xs={6} />
       <CPlaceholder xs={8} />
     </CPlaceholder>
-    <CPlaceholder as={CButton} disabled href="#" tabIndex={-1} xs={6}></CPlaceholder>
+    <CPlaceholder as={CButton} color="primary" disabled href="#" tabIndex={-1} xs={6}></CPlaceholder>
   </CCardBody>
 </CCard>
 ```
@@ -70,7 +70,7 @@ We apply additional styling to `CButton`s via `::before` to ensure the `height`
 <p aria-hidden="true">
   <CPlaceholder xs={6} />
 </p>
-<CPlaceholder as={CButton} aria-hidden="true" disabled href="#" tabIndex={-1} xs={4}></CPlaceholder>
+<CPlaceholder as={CButton} color="primary" aria-hidden="true" disabled href="#" tabIndex={-1} xs={4}></CPlaceholder>
 ```
 
 <Callout className="mb-4" color="info">