Update dreamfactory/df-graphql requirement from ~0.3 to ~0.4

Updates the requirements on [dreamfactory/df-graphql](https://github.com/dreamfactorysoftware/df-graphql) to permit the latest version.
- [Release notes](https://github.com/dreamfactorysoftware/df-graphql/releases)
- [Changelog](https://github.com/dreamfactorysoftware/df-graphql/blob/master/CHANGELOG.md)
- [Commits](dreamfactorysoftware/df-graphql@0.3.0...0.4.0)

---
updated-dependencies:
- dependency-name: dreamfactory/df-graphql
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

composer.json

@@ -32,7 +32,7 @@
   "prefer-stable":     true,
   "require":     {
     "dreamfactory/df-core": "~0.24",
-    "dreamfactory/df-graphql": "~0.3"
+    "dreamfactory/df-graphql": "~0.4"
   },
   "require-dev": {
     "phpunit/phpunit": "@stable"