[commit: ghc] master: Bump version of stm submodule back to 2.4 (7272566)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/ghc

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/727256680c8547282bda09dffefba01f9db98d1e/ghc

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commit 727256680c8547282bda09dffefba01f9db98d1e
Author: Ben Gamari <ben at smart-cactus.org>
Date:   Sat Jun 2 21:07:43 2018 -0400

    Bump version of stm submodule back to 2.4
    
    Haskeline doesn't have its upper bound lifted yet.


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727256680c8547282bda09dffefba01f9db98d1e
 libraries/stm | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libraries/stm b/libraries/stm
index 8c4d0fa..b2af9b4 160000
--- a/libraries/stm
+++ b/libraries/stm
@@ -1 +1 @@
-Subproject commit 8c4d0fabb15ad00beb1e15d027825c78b2c39881
+Subproject commit b2af9b4bb23cd2fc0b5d731b5614cdc90e7dda41