minor code comment comma grammar fixes

archive.php

@@ -79,7 +79,7 @@ get_header(); ?>
 
 				<?php
 					/* Include the Post-Format-specific template for the content.
-					 * If you want to override this in a child theme then include a file
+					 * If you want to override this in a child theme, then include a file
 					 * called content-___.php (where ___ is the Post Format name) and that will be used instead.
 					 */
 					get_template_part( 'content', get_post_format() );

comments.php

@@ -43,7 +43,7 @@ if ( post_password_required() )
 			<?php
 				/* Loop through and list the comments. Tell wp_list_comments()
 				 * to use _s_comment() to format the comments.
-				 * If you want to override this in a child theme then you can
+				 * If you want to override this in a child theme, then you can
 				 * define _s_comment() and that will be used instead.
 				 * See _s_comment() in inc/template-tags.php for more.
 				 */

index.php

@@ -23,7 +23,7 @@ get_header(); ?>
 
 				<?php
 					/* Include the Post-Format-specific template for the content.
-					 * If you want to override this in a child theme then include a file
+					 * If you want to override this in a child theme, then include a file
 					 * called content-___.php (where ___ is the Post Format name) and that will be used instead.
 					 */
 					get_template_part( 'content', get_post_format() );