請問，按照視頻改寫的 pom.xml

提示錯誤信息是：

Project build error: Non-resolvable import POM: Failure to find org.springframework:spring-framework-bom:pom:$(spring.version) in http://maven.aliyun.com/nexus/

?content/repositories/central was cached in the local repository, resolution will not be reattempted until the update interval of alimaven has elapsed or updates are forced

注釋掉 <type>pom</type> 則不報錯，請問原因。

謝謝！