Fix support for Perl 5.6.2

As a second argument for 'first' is expected list. Perl 5.6.2 parser
incorrectly thinks that qw/.../ is not list.

So use explicit list of values instead of qw operator.

.travis.yml

@@ -1,5 +1,6 @@
 language: perl
 perl:
+  - "5.6.2"
   - "5.8"
   - "5.10"
   - "5.12"

lib/Test2/API/InterceptResult/Squasher.pm

@@ -29,7 +29,7 @@ sub can_squash {
     return unless $event->has_info;
 
     # Do not merge up if one of these is true
-    return if first { $event->$_ } qw/causes_fail has_assert has_bailout has_errors has_plan has_subtest/;
+    return if first { $event->$_ } 'causes_fail', 'has_assert', 'has_bailout', 'has_errors', 'has_plan', 'has_subtest';
 
     # Signature if we can squash
     return $event->trace_signature;