Update to MathOptFormat v0.5

[odow]

x-ref: jump-dev/MathOptFormat#14

[odow]

Any other changes we want?

[blegat]

What is going to happen when you try to read an old file with the new MOI ? It will print an error message saying that the version does not match ?

[odow]

Ah. Good catch. This piece of code doesn't really make sense:

MathOptInterface.jl/src/FileFormats/MOF/read.jl

Lines 16 to 22 in 284ab04

	if file_version > VERSION
	error(
	"Sorry, the file can't be read because this library supports " *
	"v$(VERSION) of MathOptFormat, but the file you are trying to " *
	"read is v$(file_version)."
	)
	end

Hold off merging, and I will push a fix.