Add graphql to parser options in help output (#2519)

bin/prettier.js

@@ -302,7 +302,7 @@ if (
       "  --jsx-bracket-same-line  Put > on the last line instead of at a new line.\n" +
       "  --trailing-comma <none|es5|all>\n" +
       "                           Print trailing commas wherever possible. Defaults to none.\n" +
-      "  --parser <flow|babylon|typescript|postcss|json>\n" +
+      "  --parser <flow|babylon|typescript|postcss|json|graphql>\n" +
       "                           Specify which parse to use. Defaults to babylon.\n" +
       "  --cursor-offset <int>    Print (to stderr) where a cursor at the given position would move to after formatting.\n" +
       "                           This option cannot be used with --range-start and --range-end\n" +