doc: Add missing comma between optional and author

README

@@ -76,7 +76,7 @@ To enable optional functionality or programs, this software might be needed:
 To run the test suite («make check»):
 
   IO-String perl module (optional)
-  Test::MinimumVersion perl module (optional author)
+  Test::MinimumVersion perl module (optional, author)
   Test::Pod perl module (optional)
   Test::Spelling perl module (optional, author)
   Test::Strict perl module (optional)