Package 'openjdk-7-jdk' has no installation candidate

[ivanrome]

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Hello,

Actually bthe build crash when trying to install openjdk-7

Package openjdk-7-jdk is not available, but is referred to by another package. This may mean that the package is missing, has been obsoleted, or is only available from another source

E: Package 'openjdk-7-jdk' has no installation candidate

https://github.com/pictolearn/docker-tutorial/blob/875ddd62c7c4e8739962efb41dba88ea2e9d9591/Usecase-5/tomcat7-jdk7/Dockerfile#L45