generator: Add missing space before class name

[kevinji]

Fixes #338. I tested this locally by generating the docs for Ppxlib_traverse_builtins and it seemed to have inserted the space.

[aantron]

Thanks!

Would you mind adding two tests where this new space is needed? It should be as easy as adding two more declarations to class.mli:

odoc/test/html/cases/class.mli

Lines 1 to 20 in d6999cc

	class type empty =
	object
	end
	class type mutually =
	object
	end
	and recursive =
	object
	end
	class mutually' : mutually
	and recursive' : recursive
	class type virtual empty_virtual =
	object
	end
	class virtual empty_virtual' : empty

something like class ['a] polymorphic (* ... *) and class type ['a] polymorphic (* ... *), then running make test, and following the instructions again to replace the output with the new one.

[kevinji]

Done, thanks for the guidance.

[aantron]

Thanks again.