Feature/update travis ci

[jackson15j]

Blind coding to try and fix the deprecation notice that is failing builds in CI.

...
Done (Total of 2 files compiled, 1 skipped)
Package `s-1.12.0' deleted.
Wrote /home/travis/.emacs.d/.cask/24.3/bootstrap/s-20180406.808/s.el
File exists: /home/travis/.emacs.d/.cask/24.3/bootstrap/s-20180406.808/s-pkg.el

!!!
!!!                    DEPRECATION NOTICE
!!!
!!!
!!!    The cask `go` script will be removed on 2021/06/01.
!!!
!!!    This is due to security concerns about the way python is
!!!    invoked from curl, and to remove the python dependency from cask.
!!!
!!!    The way to install cask without depending on the `go` script
!!!    is very simple.  Just clone Cask and pass the PATH.
!!!
!!!        git clone https://github.com/cask/cask ~/.cask
!!!        PATH=$HOME/.cask/bin:$PATH
!!!
!!!        # If you want to make it permanent
!!!        echo 'PATH=$HOME/.cask/bin:$PATH' >> .bashrc
!!!

Cask could not be bootstrapped. Try again later, or report an issue at https://github.com/cask/cask/issues
The command "curl -fsSkL https://gist.github.com/rejeep/ebcd57c3af83b049833b/raw > travis.sh && source ./travis.sh" failed and exited with 1 during .

Your build has been stopped.

[jackson15j]

Got Travis working but dropped support for 24.5. See comment in commit: d2d92b8. Here's my local travis run: https://travis-ci.com/github/jackson15j/pyvenv/builds/233797887.