Your requirements could not be resolved to an installable set of packages.
以下错误可以这样解决：
安装最新的composer-asset-plugin
composer global require "fxp/composer-asset-plugin"
Your requirements could not be resolved to an installable set of packages.
Problem 1
- yiisoft/yii2 2.0.21 requires bower-asset/jquery 3.4.*@stable | 3.3.*@stable | 3.2.*@stable | 3.1.*@stable | 2.2.*@stable | 2.1.*@stable | 1.11.*@stable | 1.12.*@stable -> no matching package found.
- yiisoft/yii2 2.0.20 requires bower-asset/jquery 3.4.*@stable | 3.3.*@stable | 3.2.*@stable | 3.1.*@stable | 2.2.*@stable | 2.1.*@stable | 1.11.*@stable | 1.12.*@stable -> no matching package found.
- yiisoft/yii2 2.0.19 requires bower-asset/jquery 3.4.*@stable | 3.3.*@stable | 3.2.*@stable | 3.1.*@stable | 2.2.*@stable | 2.1.*@stable | 1.11.*@stable | 1.12.*@stable -> no matching package found.
- yiisoft/yii2 2.0.18 requires bower-asset/jquery 3.3.*@stable | 3.2.*@stable | 3.1.*@stable | 2.2.*@stable | 2.1.*@stable | 1.11.*@stable | 1.12.*@stable -> no matching package found.
- yiisoft/yii2 2.0.17 requires bower-asset/jquery 3.3.*@stable | 3.2.*@stable | 3.1.*@stable | 2.2.*@stable | 2.1.*@stable | 1.11.*@stable | 1.12.*@stable -> no matching package found.
- yiisoft/yii2 2.0.16.1 requires bower-asset/jquery 3.3.*@stable | 3.2.*@stable | 3.1.*@stable | 2.2.*@stable | 2.1.*@stable | 1.11.*@stable | 1.12.*@stable -> no matching package found.
- yiisoft/yii2 2.0.16 requires bower-asset/jquery 3.3.*@stable | 3.2.*@stable | 3.1.*@stable | 2.2.*@stable | 2.1.*@stable | 1.11.*@stable | 1.12.*@stable -> no matching package found.
- yiisoft/yii2 2.0.15.1 requires bower-asset/jquery 3.2.*@stable | 3.1.*@stable | 2.2.*@stable | 2.1.*@stable | 1.11.*@stable | 1.12.*@stable -> no matching package found.
- yiisoft/yii2 2.0.15 requires bower-asset/jquery 3.2.*@stable | 3.1.*@stable | 2.2.*@stable | 2.1.*@stable | 1.11.*@stable | 1.12.*@stable -> no matching package found.
- Installation request for yiisoft/yii2 >=2.0.15 -> satisfiable by yiisoft/yii2[2.0.15, 2.0.15.1, 2.0.16, 2.0.16.1, 2.0.17, 2.0.18, 2.0.19, 2.0.20, 2.0.21].
