ghci: tweak option list indentation in ':show packages'

Summary:
Caught by './validate --slow' in 'ghci/scripts/ghci024'.

Commit 207875293fea07aa90efe215369629b657d1875a changed indentation a bit:

    --- ./ghci/scripts/ghci024.stdout       2014-07-31 12:05:34.000000000 +0300
    +++ ./ghci/scripts/ghci024.run.stdout   2014-08-07 17:19:23.000000000 +0300
    @@ -33,4 +33,4 @@
     active package flags: none
     ~~~~~~~~~~ Testing :show packages, including the ghc package
     active package flags:
    -  -package ghc
    +-package ghc

Patch restores indentation.

Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>

Test Plan: passed validate, tested manually

Reviewers: austin, ezyang

Reviewed By: ezyang

Subscribers: phaskell, simonmar, relrod, ezyang, carter

Differential Revision: https://phabricator.haskell.org/D126