Add graphql-mode auto installation

core/prelude-packages.el

@@ -158,6 +158,7 @@ PACKAGE is installed only if not already present.  The file is opened in MODE."
     ("\\.erl\\'" erlang erlang-mode)
     ("\\.feature\\'" feature-mode feature-mode)
     ("\\.go\\'" go-mode go-mode)
+    ("\\.graphql\\'" graphql-mode graphql-mode)
     ("\\.groovy\\'" groovy-mode groovy-mode)
     ("\\.haml\\'" haml-mode haml-mode)
     ("\\.hs\\'" haskell-mode haskell-mode)