Fix RT#131025 which is due to Build.pm failing to install docs under

'share' type path but .perl6 instead due to assumption about order of
repo-chain. We now search for 'site' explicitly.

Author: stmuk

Build.pm

@@ -7,7 +7,7 @@ use File::Find;
 class Build {
     method build($workdir) {
         my $doc-dir   = $workdir.IO.child('doc');
-        my $dest-pref = $*REPO.repo-chain.first(*.?can-install).prefix.child("doc");
+        my $dest-pref = $*REPO.repo-chain.grep(/site/).first.prefix.child("doc");
         mkdir($dest-pref) unless $dest-pref.d;
 
         my @files = find(dir => "$workdir/doc", type => 'file').list;