Changed order of calloc args to match stdlib

[robybeen]

Although it is currently working, it's worth to stick with the stdlib definition to avoid further problems

[coveralls]

Coverage remained the same at 84.213% when pulling 5d9b8e0 on robybeen:master into 6afcf16 on json-c:master.

[hawicz]

eh... "further problems" seem quite unlikely, but I guess if you're on a system that cares about alignment, and that won't give you a maximally aligned chunk of memory when the second argument to calloc is small, then perhaps this might help. Doesn't hurt, so I'll merge it.