Use HTTPS in ZEPPELIN_INTERPRETER_DEP_MVNREPO

It would be nice to have the default value of ZEPPELIN_INTERPRETER_DEP_MVNREPO set to https://repo1.maven.org/maven2/ , with HTTPS rather than HTTP, as HTTPS is now required.

Pointing to the HTTP URL returns error "501 HTTPS Required".

For more information: More information at https://links.sonatype.com/central/501-https-required.

If already done, the configuration documentation for 0.9.0 needs to be updated.