[HASKELL] Update to newer servant version

[loewenstein]

Description

Looking at taken from https://www.stackage.org/package/servant

LTS Haskell 7.8:	0.8.1
Stackage Nightly 2016-11-09:	0.9.1.1
Latest on Hackage:	0.9.1.1

shows we are one behind stack LTS and even two behind Hackage.

Swagger-codegen version

master

[wing328]

@loewenstein may I know if you have time to contribute the enhancement?

Here is a good starting point: https://github.com/swagger-api/swagger-codegen/blob/master/modules/swagger-codegen/src/main/resources/haskell-servant/stack.mustache

[wing328]

cc @algas

[wing328]

Closed via #5061

Thanks for the PR from @mandrean