Update drop-down.md

As per comment from issue: Change in Dropdown MicrosoftDocs#245

I have updated the Style Guide with the term Dropdown without hyphen.

styleguide/a-z-word-list-term-collections/d/drop-down.md

@@ -1,20 +1,20 @@
 ---
-title: drop-down - Microsoft Style Guide
+title: dropdown - Microsoft Style Guide
 author: pallep
 ms.author: pallep
 ms.date: 05/17/2018
 ms.topic: article
 ms.prod: non-product-specific
 ---
 
-# drop-down
+# dropdown
 
-It's OK to use *drop-down* as an adjective in content for developers if you need to describe the type of UI item or how it works.
+It's OK to use *dropdown* as an adjective in content for developers if you need to describe the type of UI item or how it works.
 
 **Examples**  
-a drop-down menu  
-a drop-down combo box  
-a drop-down list box 
+a dropdown menu  
+a dropdown combo box  
+a dropdown list box 
 
 For other audiences, use *box* if you must name the UI element.