Harden example script to not crash on blank lines in input

http://colabti.org/irclogger/irclogger_log/perl6?date=2018-09-15#l465

Author: zoffixznet

doc/Language/101-basics.pod6

@@ -35,7 +35,8 @@ Here's one way to solve that problem in Perl 6:
     my %matches;
     my %sets;
 
-    for $file.lines -> $line {
+    # The .grep(?*) portion filters out empty lines
+    for $file.lines.grep(?*) -> $line {
         my ($pairing, $result) = $line.split(' | ');
         my ($p1, $p2)          = $pairing.words;
         my ($r1, $r2)          = $result.split(':');