- Use http://yaml-online-parser.appspot.com/ to make sure it is valid yaml.
  http://lint.travis-ci.org/ is recommended elsewhere but does not give helpful
  error reports.
- Make sure all of your "-" lines start on the same column
- Make sure all of your "if" lines are aligned with the "else" and "fi" lines
- Recommend using tab stops (but not tab chars) everywhere for alignment
- "If" blocks must be on one travis statement and have semicolons at the
  end of each line:

```
    -   if [[ $TRAVIS_PYTHON_VERSION == 2.7 ]]; then
            echo "2.7";
        else
            echo "Not 2.7";
        end
```

- "If" blocks cannot contain comments
- All travis commands are run with `eval` and quotes are taken as literal
  characters unless you wrap the whole line in quotes:
`echo "hello : world"` is interpreted as `echo \"hello : world\"`
`"echo 'hello : world'"` is interpreted as `echo 'hello : world'`
`"echo 'hello : '$(MYVAR)'world'"` is interpreted as
  `echo 'hello : $(MYVAR)world'`
- Use `travis_retry` before a command to have it try several times before
failing (useful for installing from third party sources)
- Feel free to cancel a build rather than waiting for it to go to completion
  if you have made a change to that branch.
- A VM with 64bit Ubuntu 12.04 is a huge help.