Revert "Remove unused "exports" variable for makePublicAPI"

This reverts commit fe586d41b07df5758cae9e4378b0ea3919796484.

AMD will pass require, exports, module in that order to makePublicAPI
pass module.exports rather than exports

makePublicAPI needs to receive require, exports, and module in that order to work with AMD.

since isNode tests for module and module.exports, pass module.exports to makePublicAPI to avoid needing to test for
exports as well.
Merge pull request #530 from neonstalwart/fix-amd

revert fe586d4 and find another way to address #507