Use stable version of Slim 3

dopesong · dopesong · commit c5df61f10662 · 2015-12-07T23:14:04.000+02:00
diff --git a/composer.json b/composer.json
@@ -20,6 +20,6 @@
     },
   "require-dev": {
     "phpunit/phpunit": "^4.0",
-    "slim/slim" : "^3.0-RC2"
+    "slim/slim" : "~3.0"
   }
 }
