Fix FloatDomainError for Memory Usage

The Heroku API returns a `'1'` or `'2'` based on the web dyno's size and the result was not being typecast into an integer. Multiplying the string by the `BASE_DYNO_SIZE` would raise `FloatDomainError: Infinity` when trying to convert it to a human readable format. The visible result was a blank value for total available memory.

This fixes that. :+1: