add browser field to support browserify
add browser field to support browserify

Allows for superagent to be used with browserify (or other browser
field compatible packaging tools).

brainbytes/superagent,philipshurpik/superagent,sutoiku/superagent,KuroGuo/suberagent,deltreey/superagent,stanzi83/superagent,sebastianvera/superagent,zsh2938/superagent,KuroGuo/suberagent,soyuka/superagent,visionmedia/superagent,sutoiku/superagent,soyuka/superagent,yussan/superagent,zsh2938/superagent,modulexcite/superagent,visionmedia/superagent,reinaldo13/superagent,kmalakoff/superagent-ls,brotchie/superagent,alinz/superagent,h1bomb/superagent,classdojo/superagent,focusaurus/superagent,stasha/superagent,brainbytes/superagent,noikiy/suberagent,fredigato/superagent,modulexcite/superagent,philipshurpik/superagent,mvanlonden/superagent-webpack-client,visionmedia/superagent,KingMario/superagent,ertrzyiks/superagent,simonvizzini/superagent,deltreey/superagent,nemisj/superagent,yeatszhang/superagent,simonvizzini/superagent,geminiyellow/superagent,killerlayup/superagent,noikiy/suberagent,wushuyi/superagent,mvanlonden/superagent-webpack-client,brotchie/superagent,yeatszhang/superagent,jarvisaoieong/superagent,KingMario/superagent,ertrzyiks/superagent,craigspaeth/superagent,eligolding/superagent,stanzi83/superagent,fredigato/superagent,andyburke/superagent,ccapndave/superagent,h1bomb/superagent,ccapndave/superagent,drinks/superagent,eligolding/superagent,puterakahfi/superagent,focusaurus/superagent,andyburke/superagent,drinks/superagent,reinaldo13/superagent,bevacqua/superagent,aaroncrows/superagent,RubenVerborgh/superagent,targos/superagent,thejameskyle/superagent,targos/superagent,sebastianvera/superagent,RubenVerborgh/superagent,geminiyellow/superagent,yussan/superagent,killerlayup/superagent,thejameskyle/superagent,nemisj/superagent,craigspaeth/superagent,alinz/superagent,stasha/superagent,jarvisaoieong/superagent,wushuyi/superagent,puterakahfi/superagent,aaroncrows/superagent,classdojo/superagent,kmalakoff/superagent-ls