Browser option error

[Antonio-Laguna]

Hey here,

It seems 3.0.1 introduces a regression on this plugin regarding the browser option. One of the checks is like this:

else if (options.browser && pkg[ 'browser' ][ pkg[ 'main' ] ]) {

Which looks rather unsafe to me. If for some reason pkg['browser'] is not there, this just blows as it can read property of undefined. Was this intentional? Am I doing something wrong? Or is this a legit bug?

Kind to submit a PR to make that if a tad safer.

[Antonio-Laguna]

#129 seems like it fixed it.