Fix Illegal string offset 'orderby'

This should fix the issue mentioned in these support forum post:

https://wordpress.org/support/topic/fix-ensure-args-values-are-set-in-get_terms
https://wordpress.org/support/topic/illegal-string-offset-orderby-1
https://wordpress.org/support/topic/errors-under-php54
https://wordpress.org/support/topic/illegal-string-offset-orderby

I've had to update my GitHub repp to version 1.1.5 but the actual change is here:
https://github.com/benhuson/custom-taxonomy-sort/commit/cb5153610312c739202cd331721944e228cb4eca