Revert "Use "$@" instead of eval "$@" in travis_retry"

This reverts commit 30109b352a124ca78246b78911a6c3b87b743deb.

This ended up breaking things in production, for example git clone
didn't work:

$ git clone --depth=50 --branch=travis git://github.com/owner/repo.git owner/repo
/home/travis/build.sh: line 174: git clone --depth=50 --branch=branch_name git://github.com/owner/repo.git owner/repo: No such file or directory