{
    "name": "stack/session",
    "description": "Session stack middleware.",
    "keywords": ["stack", "session"],
    "license": "MIT",
    "authors": [
        {
            "name": "Igor Wiedler",
            "email": "igor@wiedler.ch"
        }
    ],
    "require": {
        "php": ">=5.4.0",
        "pimple/pimple": "~1.0@dev",
        "symfony/http-foundation": "~2.1",
        "symfony/http-kernel": "~2.1"
    },
    "require-dev": {
        "silex/silex": "~1.0@dev",
        "stack/builder": "~1.0@dev",
        "stack/callable-http-kernel": "~1.0@dev",
        "symfony/browser-kit": "~2.1"
    },
    "autoload": {
        "psr-0": { "Stack": "src" }
    },
    "extra": {
        "branch-alias": { "dev-master": "1.0-dev" }
    }
}

{
    "name": "stack/session",
    "description": "Session stack middleware.",
    "keywords": ["stack", "session"],
    "license": "MIT",
    "authors": [
        {
            "name": "Igor Wiedler",
            "email": "igor@wiedler.ch"
        }
    ],
    "require": {
        "php": ">=5.4.0",
        "pimple/pimple": "2.0*",
        "symfony/http-foundation": "~2.1",
        "symfony/http-kernel": "~2.1"
    },
    "require-dev": {
        "silex/silex": "~1.0@dev",
        "stack/builder": "~1.0@dev",
        "stack/callable-http-kernel": "~1.0@dev",
        "symfony/browser-kit": "~2.1"
    },
    "autoload": {
        "psr-0": { "Stack": "src" }
    },
    "extra": {
        "branch-alias": { "dev-master": "1.0-dev" }
    }
}

Update pimple to version 2.0.
Update pimple to version 2.0.