Update to aeson-2.0.3.0

2.0.3.0
* text-2.0 support
* bytestring-0.11.2.0 support
* Rewrite pure text literal unescaper.
* Add QuickCheck's Arbitrary, CoArbitrary and Function instances

2.0.2.0
* Add IsList (KeyMap v) instance.
* Add toMapText and fromMapText to Data.Aeson.KeyMap.
* Add ShortText instances
* Add Solo instances

2.0.1.0
* Add FromJSON KeyMap instance.
* Make ordered-keymap on by default.

2.0.0.0
* Remove forced -O2 and then unneeded fast flag. Also remove most of INLINE
  pragmas. In the effect, aeson compiles almost twice as fast.
* To get fast compilation effect cabal-install users may specify
  optimization: False.
* Make map type used by Object abstract so the underlying implementation
  can be modified, thanks to Callan McGill
* Add ordered-keymap flag allowing to change the underlying implementation
  of object KeyMap.
* Drop GHC-7 support
* Remove Data.Aeson.Encode module
* Double and Float infinities are encoded as "+inf" and "-inf". Change
  To/FromJSONKey instances to use "+inf" and "-inf" too.
* FromJSON () and FromJSON (Proxy tag) accept any JSON value.

(pho)