fix(junitoutputconf): fix the specs paths in the example config to output junit xml
fix(element): fix an error where all.then() wasn't calling callbacks.

Closes #267
docs(getting-started): fix control-flow link
feat(runner): add error message for bad jar path

Closes #259.
If a bad path was provided in the protractor
configuration, the runner would fail with an
ambiguous error.
This fix checks that a file exists at the
provided path, and throws an error if not,
suggesting that perhaps the version is
wrong in the configuration.