[GHC] #13808: Bump Cabal submodule

[GHC]

#13808: Bump Cabal submodule
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        Reporter:  bgamari           |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:  8.2.1
       Component:  Compiler          |              Version:  8.2.1-rc2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by refold):

 [https://github.com/haskell/cabal/releases/tag/Cabal-v2.0.0.1
 Cabal-v2.0.0.1 tag] has been created.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13808#comment:1>
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