Some people use git: depth: False in thier Travis CI config, most

commonly because tests may need full access to the repository history.

In this case, we were still including git checkout --unshallow in the

build script, which wasn't fatal but produced ugly warnings. This change

checks for a full-repo checkout in the Travis config and only adds the

checkout if necessary.

Created a Travis integration that included git: depth: False in the

config. Saw that prior to this change, an ugly error was shown in the

build log, and after everything was fine.