Update durandal.d.ts

mapNav's second and third parameters must be optional..
Merge pull request #440 from Diullei/master

commit breeze reverted. I need to solve some bugs
Merge pull request #441 from Diullei/master

breeze updated - 1.2.7
Merge pull request #438 from arash16/patch-1

Update durandal.d.ts --> router.mapNav's second and third parameters must be optional
resolved conflicts to pullrequest #387