They actually don't provide a justification. That blog makes the argument that omitting them is harmless. Neither GitHub nor the blog make an argument for why you should omit them, however.
Do you use semicolons in Ruby, Python, shell, or other semicolon-less language where semicolons are allowed? If not, what's your justification for omitting them?
Why is a justification needed?
The justification is to be idiomatic and match the bulk of existing code.
Yeah you're right. There's no solid reason to do so, in the face of a solid reason not to.