Fix yml type (#225)

Schema validation: Incompatible types.
Required: boolean. Actual: string.

Author: Rotzbua

_config.yml

@@ -30,12 +30,12 @@ exclude_from_localizations: ["assets"]
 # Collections
 collections:
   documentation:
-    output: "true"
+    output: true
   blog:
-    output: "true"
+    output: true
     permalink: /blog/:year/:month/:slug
   events:
-    output: "true"
+    output: true
     permalink: /events/:year/:month/:title
 
 defaults: