perldelta: Revise wording

Some of this was suggested by Jarkko Hietaniemi

Author: khwilliamson

pod/perldelta.pod

@@ -304,10 +304,10 @@ This empty function call now takes about a third less time to execute:
 =item *
 
 Many languages, such as Chinese, are caseless.  Perl now knows about
-most modern commercially important ones, and skips much of the work when
+most common ones, and skips much of the work when
 a program tries to change case in them (like C<ucfirst()>) or match
 caselessly (C<qr//i>).  This will speed up a program, such as a web
-server, that can operate on multiple languages, while operating on a
+server, that can operate on multiple languages, while it is operating on a
 caseless one.
 
 =item *