Update test/perl/README to insist on Perl version >= 5.8.3, too.

Oversight in previous commit, noted by Daniel Gustafsson.

Discussion: https://postgr.es/m/87y278s6iq.fsf@wibble.ilmari.org

Author: tglsfdc

src/test/perl/README

@@ -73,13 +73,13 @@ perldoc for the test modules, e.g.:
 Required Perl
 -------------
 
-Tests must run on perl 5.8.0 and newer. perlbrew is a good way to obtain such
+Tests must run on perl 5.8.3 and newer. perlbrew is a good way to obtain such
 a Perl; see http://perlbrew.pl .
 
 Just install and
 
-    perlbrew --force install 5.8.0
-    perlbrew use 5.8.0
+    perlbrew --force install 5.8.3
+    perlbrew use 5.8.3
     perlbrew install-cpanm
     cpanm install IPC::Run