Set requirements for a 3.0 version

composer.json

@@ -15,7 +15,7 @@
     "require": {
         "aws/aws-sdk-php": "2.*",
         "doctrine/cache": "1.*",
-        "silverstripe/crontask": "*"
+        "silverstripe/crontask": "~0.9-dev"
     },
     "extra": {
         "installer-name": "aws"