Update dreamfactory/df-oauth requirement from ~0.15 to ~0.16

Updates the requirements on [dreamfactory/df-oauth](https://github.com/dreamfactorysoftware/df-oauth) to permit the latest version.
- [Release notes](https://github.com/dreamfactorysoftware/df-oauth/releases)
- [Changelog](https://github.com/dreamfactorysoftware/df-oauth/blob/master/CHANGELOG.md)
- [Commits](dreamfactorysoftware/df-oauth@0.15.0...0.16.0)

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

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

composer.json

@@ -34,7 +34,7 @@
   "minimum-stability": "dev",
   "prefer-stable": true,
   "require":     {
-    "dreamfactory/df-oauth": "~0.15",
+    "dreamfactory/df-oauth": "~0.16",
     "phpseclib/phpseclib": "2.0.*"
   },
   "autoload":    {