Update development dependencies

composer.json

@@ -6,17 +6,17 @@
     "license": "BSD-3-Clause",
     "require": {
         "silverstripe/recipe-plugin": "^1.2",
-        "silverstripe/recipe-core": "4.6.x-dev",
-        "silverstripe/admin": "1.6.x-dev",
-        "silverstripe/asset-admin": "1.6.x-dev",
-        "silverstripe/campaign-admin": "1.6.x-dev",
-        "silverstripe/versioned-admin": "1.6.x-dev",
-        "silverstripe/cms": "4.6.x-dev",
-        "silverstripe/errorpage": "1.6.x-dev",
-        "silverstripe/graphql": "3.3.x-dev",
-        "silverstripe/reports": "4.6.x-dev",
-        "silverstripe/siteconfig": "4.6.x-dev",
-        "silverstripe/versioned": "1.6.x-dev"
+        "silverstripe/recipe-core": "4.6.0-rc1",
+        "silverstripe/admin": "1.6.0-rc1",
+        "silverstripe/asset-admin": "1.6.0-rc1",
+        "silverstripe/campaign-admin": "1.6.0-rc1",
+        "silverstripe/versioned-admin": "1.6.0-rc1",
+        "silverstripe/cms": "4.6.0-rc1",
+        "silverstripe/errorpage": "1.6.0-rc1",
+        "silverstripe/graphql": "3.3.0-rc1",
+        "silverstripe/reports": "4.6.0-rc1",
+        "silverstripe/siteconfig": "4.6.0-rc1",
+        "silverstripe/versioned": "1.6.0-rc1"
     },
     "require-dev": {
         "phpunit/phpunit": "^5.7",
@@ -33,4 +33,4 @@
     },
     "prefer-stable": true,
     "minimum-stability": "dev"
-}
+}