### Please describe the problem.
git-annex doesn't build if the aws dependency is version 0.17.1

This probably wasn't caught during your testing because the stack.yaml is currently set to use aws-0.16.

### What steps will reproduce the problem?
cabal install with --flags=s3\ webapp

### What version of git-annex are you using? On what operating system?
6.20171003 on macOS

### Please provide any additional information below.

The error is

[[!format sh """
[327 of 580] Compiling Remote.Helper.Http ( Remote/Helper/Http.hs, dist/dist-sandbox-69bd6735/build/git-annex/git-annex-tmp/Remote/Helper/Http.o )
[328 of 580] Compiling Remote.WebDAV    ( Remote/WebDAV.hs, dist/dist-sandbox-69bd6735/build/git-annex/git-annex-tmp/Remote/WebDAV.o )
[329 of 580] Compiling Remote.S3        ( Remote/S3.hs, dist/dist-sandbox-69bd6735/build/git-annex/git-annex-tmp/Remote/S3.o )

Remote/S3.hs:501:57: error:
    • Couldn't match expected type ‘AWS.Configuration’
                  with actual type ‘Maybe
                                      http-client-0.5.7.0:Network.HTTP.Client.Types.Proxy
                                    -> AWS.Configuration’
    • Probable cause: ‘awscfg’ is applied to too few arguments
      In the second argument of ‘S3Handle’, namely ‘awscfg’
      In the second argument of ‘($)’, namely ‘S3Handle mgr awscfg s3cfg’
      In the second argument of ‘($)’, namely
        ‘Just $ S3Handle mgr awscfg s3cfg’
    |
501 |                                 a $ Just $ S3Handle mgr awscfg s3cfg
    |                                                         ^^^^^^
cabal: Leaving directory '.'
cabal: Error: some packages failed to install:
git-annex-6.20171003-5GFRliFOEl0KqDuhwYRTdH failed during the building phase.
The exception was:
ExitFailure 1
"""]]

Full build log is here: https://gist.github.com/ilovezfs/661a158dbe8aac33802f9b43eb150539

### Have you had any luck using git-annex before? (Sometimes we get tired of reading bug reports all day and a lil' positive end note does wonders)

Yes! :)

> [[fixed|done]] --[[Joey]]
