Switch from "posts" to "documents"

The Apertis website isn't a blog, switch from the "posts" terminology to
"documents" which is much more inline with what we have on the site.

Signed-off-by: Martyn Welch <martyn.welch@collabora.com>

themes/apertis/i18n/en.yaml

@@ -10,13 +10,13 @@
 - id: readMore
   translation: "Read More"
 - id: olderPosts
-  translation: "Older Posts"
+  translation: "Older Documents"
 - id: newerPosts
-  translation: "Newer Posts"
+  translation: "Newer Documents"
 - id: previousPost
-  translation: "Previous Post"
+  translation: "Previous Document"
 - id: nextPost
-  translation: "Next Post"
+  translation: "Next Document"
 
 # 404 page
 - id: pageNotFound