Fix run/shell :merge
Fix run/shell :merge

Previously this command would deadlock:
`my $proc = run("ls", :merge).out.slurp.say`

lucasbuchala/rakudo,usev6/rakudo,labster/rakudo,salortiz/rakudo,raydiak/rakudo,Gnouc/rakudo,rakudo/rakudo,softmoth/rakudo,MasterDuke17/rakudo,Gnouc/rakudo,tbrowder/rakudo,jonathanstowe/rakudo,tbrowder/rakudo,nbrown/rakudo,sjn/rakudo,tony-o/rakudo,jonathanstowe/rakudo,MasterDuke17/rakudo,raydiak/rakudo,rakudo/rakudo,nbrown/rakudo,nbrown/rakudo,awwaiid/rakudo,rakudo/rakudo,sjn/rakudo,salortiz/rakudo,usev6/rakudo,softmoth/rakudo,usev6/rakudo,usev6/rakudo,lucasbuchala/rakudo,rakudo/rakudo,tbrowder/rakudo,nbrown/rakudo,salortiz/rakudo,MasterDuke17/rakudo,tony-o/rakudo,tbrowder/rakudo,labster/rakudo,tbrowder/rakudo,rakudo/rakudo,MasterDuke17/rakudo,Gnouc/rakudo,sjn/rakudo,softmoth/rakudo,softmoth/rakudo,tony-o/rakudo,tony-o/rakudo,tbrowder/rakudo,awwaiid/rakudo,nbrown/rakudo,raydiak/rakudo,nbrown/rakudo,labster/rakudo,awwaiid/rakudo,salortiz/rakudo,softmoth/rakudo,rakudo/rakudo,Gnouc/rakudo,sjn/rakudo,lucasbuchala/rakudo,tony-o/rakudo,jonathanstowe/rakudo,lucasbuchala/rakudo,MasterDuke17/rakudo,labster/rakudo,awwaiid/rakudo,usev6/rakudo,Gnouc/rakudo,Gnouc/rakudo,labster/rakudo,jonathanstowe/rakudo,MasterDuke17/rakudo,labster/rakudo,tony-o/rakudo,raydiak/rakudo,salortiz/rakudo,sjn/rakudo,awwaiid/rakudo,jonathanstowe/rakudo,salortiz/rakudo,lucasbuchala/rakudo