Modifications so that guppy can be loaded using webpack

[nishantwrp]

Added module.exports = Guppy in the build files. So, that we can do

const Guppy = require(guppy.min.js);

[seanlip]

@nishantwrp please add a clearer description explaining what modifications are being done and why.

(In general, your PR descriptions could use more detail -- please bear this in mind for future PRs. Thanks!)

[nishantwrp]

@seanlip done!

[seanlip]

Thanks, LGTM