Deleting coma from string

[WhoAmI]

Hello, i just want to know how to remove coma from string? Well, i want to delete ONLY ONE coma which is on the end of string.

Like

"Something, something, something,"

and i want

"Something, something, something"

[TAPL]

str = "Something, something, something," 
fStr = string.sub(str, 1, -2) 
print(fStr) -- > "Something, something, something" 

[WhoAmI]

Thanks.