Error on Mac configuring PyPI via Travis

## Location within the Course

* Section:4
* Lesson:4
* Language:English

## Description

In "Configure PyPI Authentication Via Travis". I'm on a Mac and installed Travis using the command `brew install travis`, but then when I did `travis encrypt --add deploy.password`, I get this message:
```
Shell completion not installed. Would you like to install it now? |y y
Detected repository as purplediane/shortbread, is this correct? |yes| yes
not logged in, please run travis login --pro
```
Then I did `travis login --pro`
It asked for username and password, which I entered, and then got:
```
no implicit conversion of nil into String
for a full error report, run travis report --pro
```
Turns out the problem has something to do with ruby versions. When I do `ruby --version`, it tells me I have 2.5.0p0, but my travis report said it is 2.0.0-p648, which is not current enough to work. Probably my Homebrew is not quite right, since I rarely use it, although I recently did `brew update` or whatever you are supposed to do to keep the Brewed things up-to-date. (I try not to be too much of a curmudgeonly luddite, but just can't get interested in Homebrew enough to spend the time to understand it; sorry, brew-lovers).

### Solution
My solution was to `brew uninstall travis` and then do `gem install travis -v 1.8.8 --no-rdoc --no-ri` per [instructions here](https://github.com/travis-ci/travis.rb#installation). Even though it claims that Ruby 2.0 is OK, others have said the problem went away after upgrading Ruby.

In any case, after installing it as a gem, the `travis encrypt` command worked.

See https://github.com/travis-ci/travis.rb/issues/190#issuecomment-369749402 for more discussion of this issue.

Maybe this can be in the FAQ or troubleshooting area, with a link from the location in 4.4 for those who have the problem.