Update to reflection-2.1.5

2.1.5 [2019.08.27]
* Fix a bug in which reifyNat would yield incorrect results for very
  large Integers on GHC 8.2 or later.

2.1.4 [2018.07.02]
* Allow building with GHC 8.6.

2.1.3 [2018.01.18]
* Add Semigroup instance for ReflectedMonoid.

2.1.2
* Support cross-compilation and unregistered GHC builds.

2.1.1.1
* Fixed typos in the documentation.

2.1.1
* Fixed support for GHC 7.0

2.1
* Added ReifiedMonoid and ReifiedApplicative.

2
* Added reifyNat and reifySymbol for GHC 7.8+, capable of reflecting
  into the KnownNat and KnownSymbol classes respectively for use with
  other APIs.
* Back-ported reifyTypeable from lens. This enables us to perform a
  (less efficient) form of Typeable reflection.

1.5.2
* Renamed the flag for disabling the use of template-haskell, to
  -f-template-haskell for consistency with my other packages.

1.5.1.2
* Builds warning-free on GHC 7.10.
* Added a dynamic FromJSON example.

1.5.1.1
* Updated the link to the paper.
* More examples.

(pho)