change raku to rakudo executable
change raku to rakudo executable

As discussed here in https://github.com/rakudo/rakudo/pull/3642
and mentioned in https://github.com/Raku/problem-solving/blob/master/solutions/language/Path-to-Raku.md#executables
rakudo is executable and raku is symlink.

Reflect that change with this commit.

salortiz/rakudo,labster/rakudo,rakudo/rakudo,nbrown/rakudo,MasterDuke17/rakudo,tbrowder/rakudo,softmoth/rakudo,salortiz/rakudo,nbrown/rakudo,tbrowder/rakudo,salortiz/rakudo,tony-o/rakudo,rakudo/rakudo,rakudo/rakudo,labster/rakudo,MasterDuke17/rakudo,labster/rakudo,MasterDuke17/rakudo,nbrown/rakudo,tbrowder/rakudo,tbrowder/rakudo,rakudo/rakudo,softmoth/rakudo,tbrowder/rakudo,labster/rakudo,softmoth/rakudo,tony-o/rakudo,softmoth/rakudo,rakudo/rakudo,tony-o/rakudo,nbrown/rakudo,tbrowder/rakudo,tony-o/rakudo,MasterDuke17/rakudo,tony-o/rakudo,salortiz/rakudo,nbrown/rakudo,MasterDuke17/rakudo,labster/rakudo,softmoth/rakudo,nbrown/rakudo,rakudo/rakudo,salortiz/rakudo,salortiz/rakudo,tony-o/rakudo,MasterDuke17/rakudo,labster/rakudo