Minimum Stability Settings

Composer accepts these flags as minimum-stability settings. The default setting for minimum-stability if not provided is assumed to be stable, but you could define any of the flags down the hierarchy.

–stable (most stable)
– RC
– beta
– alpha
– dev (least stable)

使用 @dev 解决版本问题

    "minimum-stability": "stable",
    "require": {
        "php": ">=5.4.0",
        "yiisoft/yii2": "*",
        "yiisoft/yii2-bootstrap": "*",
        "yiisoft/yii2-swiftmailer": "*",
        "kartik-v/yii2-grid": "@dev"
    },

Setting composer minimum stability for your application