Fixed metabox.php - was pre-echoing an argument to an apply_filter

Was echoing an argument to an apply_filter (via _e) rather than echoing the result of the apply_filter (with its argument submitted via __).
Merge pull request #2284 from danlester/master

Fixed metabox.php - was pre-echoing an argument to an apply_filter
Update .travis.yml
Adding more unit tests for Discount Codes including flat rates, as well as updating discounts
Function naming error
Merge pull request #2293 from cklosowski/unit-tests

Adding some more unit tests for discounts
Update discounts.php
avoiding number_format expects double error

Under some circumstances `number_format` can return an error since it expects the var type to be `double`.

Now we're casting to make sure we get the proper type of var.
Merge pull request #2306 from curtismchale/patch-1

avoiding number_format expects double error
Should solve #2310