remove the last remaining uses of base.pm

This finishes the job that 9797d9c
started but only almost finished.

lib/Plack/App/Cascade.pm

@@ -1,6 +1,6 @@
 package Plack::App::Cascade;
 use strict;
-use base qw(Plack::Component);
+use parent qw(Plack::Component);
 
 use Plack::Util;
 use Plack::Util::Accessor qw(apps catch codes);

t/Plack-Middleware/httpexceptions.t

@@ -11,16 +11,16 @@ sub throw {
 }
 
 package HTTP::Error::InternalServerError;
-use base qw(HTTP::Error);
+use parent -norequire => qw(HTTP::Error);
 sub code { 500 }
 
 package HTTP::Error::Forbidden;
-use base qw(HTTP::Error);
+use parent -norequire => qw(HTTP::Error);
 sub code { 403 }
 sub as_string { "blah blah blah" }
 
 package HTTP::Error::Redirect;
-use base qw(HTTP::Error);
+use parent -norequire => qw(HTTP::Error);
 sub code { 302 }
 sub location { "http://somewhere/else" }
 

t/Plack-Middleware/httpexceptions_streaming.t

@@ -11,11 +11,11 @@ sub throw {
 }
 
 package HTTP::Error::InternalServerError;
-use base qw(HTTP::Error);
+use parent -norequire => qw(HTTP::Error);
 sub code { 500 }
 
 package HTTP::Error::Forbidden;
-use base qw(HTTP::Error);
+use parent -norequire => qw(HTTP::Error);
 sub code { 403 }
 sub as_string { "blah blah blah" }