Make sure PouchDB works in Service Workers
Make sure PouchDB works in Service Workers

In Chromium, `XMLHttpRequest` isn't exposed to Service Workers anymore.
See https://src.chromium.org/viewvc/blink?revision=178829&view=revision.

This changes `request-browser` to fall back to the new Fetch API if
`XMLHttpRequest` is `undefined`.

elkingtonmcb/pouchdb,elkingtonmcb/pouchdb,tyler-johnson/pouchdb,microlv/pouchdb,TechnicalPursuit/pouchdb,cshum/pouchdb,willholley/pouchdb,Charlotteis/pouchdb,lukevanhorn/pouchdb,yaronyg/pouchdb,optikfluffel/pouchdb,Knowledge-OTP/pouchdb,nickcolley/pouchdb,mainerror/pouchdb,elkingtonmcb/pouchdb,lakhansamani/pouchdb,cdaringe/pouchdb,marcusandre/pouchdb,mikeymckay/pouchdb,microlv/pouchdb,mattbailey/pouchdb,garrensmith/pouchdb,willholley/pouchdb,janraasch/pouchdb,mainerror/pouchdb,garrensmith/pouchdb,KlausTrainer/pouchdb,seigel/pouchdb,johnofkorea/pouchdb,seigel/pouchdb,callahanchris/pouchdb,Knowledge-OTP/pouchdb,Actonate/pouchdb,willholley/pouchdb,cshum/pouchdb,mwksl/pouchdb,callahanchris/pouchdb,tohagan/pouchdb,garrensmith/pouchdb,shimaore/pouchdb,cdaringe/pouchdb,ramdhavepreetam/pouchdb,jhs/pouchdb,nicolasbrugneaux/pouchdb,jhs/pouchdb,adamvert/pouchdb,Charlotteis/pouchdb,nickcolley/pouchdb,Actonate/pouchdb,mwksl/pouchdb,greyhwndz/pouchdb,asmiller/pouchdb,p5150j/pouchdb,Knowledge-OTP/pouchdb,p5150j/pouchdb,janraasch/pouchdb,ramdhavepreetam/pouchdb,cesarmarinhorj/pouchdb,lukevanhorn/pouchdb,daleharvey/pouchdb,yaronyg/pouchdb,p5150j/pouchdb,callahanchris/pouchdb,pouchdb/pouchdb,crissdev/pouchdb,microlv/pouchdb,cesarmarinhorj/pouchdb,ntwcklng/pouchdb,patrickgrey/pouchdb,cdaringe/pouchdb,shimaore/pouchdb,bbenezech/pouchdb,nickcolley/pouchdb,Actonate/pouchdb,optikfluffel/pouchdb,patrickgrey/pouchdb,h4ki/pouchdb,optikfluffel/pouchdb,h4ki/pouchdb,TechnicalPursuit/pouchdb,bbenezech/pouchdb,colinskow/pouchdb,tohagan/pouchdb,bbenezech/pouchdb,jhs/pouchdb,asmiller/pouchdb,asmiller/pouchdb,mattbailey/pouchdb,lakhansamani/pouchdb,ntwcklng/pouchdb,crissdev/pouchdb,KlausTrainer/pouchdb,pouchdb/pouchdb,KlausTrainer/pouchdb,mwksl/pouchdb,tyler-johnson/pouchdb,mainerror/pouchdb,nicolasbrugneaux/pouchdb,cesarmarinhorj/pouchdb,johnofkorea/pouchdb,patrickgrey/pouchdb,lukevanhorn/pouchdb,mikeymckay/pouchdb,greyhwndz/pouchdb,yaronyg/pouchdb,marcusandre/pouchdb,lakhansamani/pouchdb,greyhwndz/pouchdb,cshum/pouchdb,mattbailey/pouchdb,colinskow/pouchdb,TechnicalPursuit/pouchdb,seigel/pouchdb,tyler-johnson/pouchdb,adamvert/pouchdb,tohagan/pouchdb,marcusandre/pouchdb,ramdhavepreetam/pouchdb,adamvert/pouchdb,colinskow/pouchdb,janraasch/pouchdb,johnofkorea/pouchdb,daleharvey/pouchdb,Dashed/pouchdb,crissdev/pouchdb,shimaore/pouchdb,Dashed/pouchdb,pouchdb/pouchdb,Dashed/pouchdb,daleharvey/pouchdb,ntwcklng/pouchdb,nicolasbrugneaux/pouchdb,h4ki/pouchdb,mikeymckay/pouchdb,Charlotteis/pouchdb