fixes typo

Author: ljarzynski

deploy-apps/manifest-attributes.html.md.erb

@@ -41,7 +41,7 @@ To add variables to an app manifest, do the following:
     memory: 1G
     ```
 
-1. Add the variables to your app manifest file using the following format: `((VARIABLE-NAME)). See the following example:
+1. Add the variables to your app manifest file using the following format: `((VARIABLE-NAME))`. See the following example:
 
     ```
     ---