Add number to list of allowed JSON input types

[nguyer]

I missed this one in the pervious merge when porting over @peterbroadhurst's changes 🙁

[codecov-commenter]

Codecov Report

Merging #23 (7853112) into main (8438aaa) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##              main       #23   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           33        33           
  Lines         2080      2081    +1     
=========================================
+ Hits          2080      2081    +1     

Impacted Files	Coverage Δ
pkg/fftypes/ffi_param_validator.go	100.00% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 8438aaa...7853112. Read the comment docs.