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ARROW-3976: [Ruby] Try to upgrade git to avoid errors caused by Homebrew on older git

It seems that `brew update` can fail if the git version is too old, see https://github.com/Linuxbrew/brew/issues/820. Also adds retry logic

Author: Kouhei Sutou <kou@clear-code.com>
Author: Wes McKinney <wesm+git@apache.org>

Closes #3155 from wesm/ARROW-3976 and squashes the following commits:

0c7964ba3 <Kouhei Sutou> Stop to use old Ruby
7dce4f0a3 <Kouhei Sutou> travis_wait isn't available in custom shell script
6d41e7196 <Kouhei Sutou> Make brew commands more robust
05044892b <Wes McKinney> Incorporate code review
8c0454fd7 <Wes McKinney> Try to upgrade git to avoid errors caused by Homebrew on older git, where --local argument is missing