THRIFT-4965: Perl tutorial server doesn't work due to the lack of use statement

Client: Perl

This closes #1885.
diff --git a/tutorial/perl/PerlServer.pl b/tutorial/perl/PerlServer.pl
index dfe6b89..ee5d936 100644
--- a/tutorial/perl/PerlServer.pl
+++ b/tutorial/perl/PerlServer.pl
@@ -23,6 +23,7 @@
 use lib '../gen-perl';
 use Thrift::Socket;
 use Thrift::Server;
+use Thrift::ServerSocket;
 use tutorial::Calculator;
 
 package CalculatorHandler;