isArray is not defined in postal.lodash.js

[Hank Hsiao]

This could be a problem, please check.
https://github.com/postaljs/postal.js/blob/master/lib/postal.lodash.js#L619

[Jim Cowart]

Looks like there's an edge case where if __postalReady__ is defined and postal tried to process the contents, the mindash version of postal will have an issue. I'm in the process of converting this project's build and module format, and plan to replace lodash methods with ES5 equivalents where possible, to minimize dependency footprint....I'll address this with those changes, thanks!