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

lib/tasks/docs.thor

@@ -267,17 +267,19 @@ class DocsCLI < Thor
 
   private
 
-  def find_docs(names)
-    names.flat_map do |name|
-      name, version = name.split(/@|~/)
-      if version == 'all'
-        Docs.find(name, false).versions
-      else
-        Docs.find(name, version)
-      end
+  def find_doc(name)
+    name, version = name.split(/@|~/)
+    if version == 'all'
+      Docs.find(name, false).versions
+    else
+      Docs.find(name, version)
     end
   end
 
+  def find_docs(names)
+    names.flat_map {|name| find_doc(name)}
+  end
+
   def find_docs_by_slugs(slugs)
     slugs.flat_map do |slug|
       slug, version = slug.split(/~/)