Fixes whitespace issues in placeholder docs

Author: weierophinney

doc/book/helpers/placeholder.md

@@ -133,15 +133,18 @@ foreach ($this->data as $datum): ?>
 
 ## Clearing Content
 
-In certain situations it is desirable to remove or clear containers and aggregated content. The placeholder view helper
-provides two methods to either delete a specific container or clear all containers at once:
+In certain situations it is desirable to remove or clear containers and
+aggregated content. The placeholder view helper provides two methods to either
+delete a specific container or clear all containers at once:
 
 ### Delete a single container
+
 ```php
 $this->plugin('placeholder')->deleteContainer('myNamedContainer');
 ```
 
 ### Clear all containers
+
 ```php
 $this->plugin('placeholder')->clearContainers();
 ```