Add @Tritlo and @solrun as authors

AUTHORS.md

@@ -0,0 +1,7 @@
+The following people have participated in creating this library, either by
+directly contributing code, by providing thoughtful input in discussions about
+the library design, or somehow else. In order of appearance:
+
+- [Danny Navarro](mailto:j@dannynavarro.net) - [@jdnavarro](https://github.com/jdnavarro)
+- [Matthías Páll Gissurarson](mailto:mpg@mpg.is) -  [@Tritlo](https://github.com/Tritlo)
+- [Sólrún Halla Einarsdóttir](mailto:she@mpg.is) - [@solrun](https://github.com/solrun)

graphql.cabal

@@ -8,7 +8,7 @@ homepage:            https://github.com/jdnavarro/graphql-haskell
 bug-reports:         https://github.com/jdnavarro/graphql-haskell/issues
 license:             BSD3
 license-file:        LICENSE
-author:              Danny Navarro
+author:              Danny Navarro, Matthías Páll Gissurarson, Sólrún Halla Einarsdóttir
 maintainer:          j@dannynavarro.net
 copyright:           Copyright (C) 2015-2016 J. Daniel Navarro
 category:            Web