Add and use a singular finder, `find_doc()`

lib/tasks/docs.thor

@@ -267,8 +267,7 @@ class DocsCLI < Thor
 
   private
 
-  def find_docs(names)
-    names.flat_map do |name|
+  def find_doc(name)
     name, version = name.split(/@|~/)
     if version == 'all'
       Docs.find(name, false).versions
@@ -276,6 +275,9 @@ class DocsCLI < Thor
       Docs.find(name, version)
     end
   end
+
+  def find_docs(names)
+    names.flat_map {|name| find_doc(name)}
   end
 
   def find_docs_by_slugs(slugs)