cannot build the sdist for lens-2.6.1

[andreabedini]

foliage seems to barf when building a sdist for lens-2.6.1, that starting point is already an sdist so this should be a no-op.

Warning: _cache/lens/2.6.1/lens.cabal:217:5: The field "other-extensions" is
available only since the Cabal specification version 1.10.
foliage: Error when running Shake build system:
  at want, called at app/Foliage/CmdBuild.hs:37:7 in main:Foliage.CmdBuild
* Depends on: buildAction
  at apply1, called at app/Foliage/PrepareSdist.hs:39:23 in main:Foliage.PrepareSdist
* Depends on: PrepareSdistRule "_cache/lens/2.6.1"
* Raised the exception:
dieVerbatim: user error (Error: foliage: properties.hs doesn't exist
)

steps to reproduce

$ cabal run -- foliage import-index --package-name lens --package-version 2.6.1
$ cabal run -- foliage build