Add max int to exports

[LeoVS09]

Feature request

GraphQL has a limit to use 32-bit max and min Integer, but js, not built-in 32-bit max Integer.
I prefer not to set constants in the project, if they already defined.

graphql-js/src/type/scalars.js

Lines 21 to 22 in f31f505

	const MAX_INT = 2147483647;
	const MIN_INT = -2147483648;

Please, add exports to contents