Update MinidumpYAML to use minidump::Exception for exception stream

Reviewers: labath, jhenderson, clayborg, MaskRay, grimar

Reviewed By: grimar

Subscribers: lldb-commits, grimar, MaskRay, hiraditya, llvm-commits

Tags: #llvm, #lldb

Differential Revision: https://reviews.llvm.org/D68657

llvm-svn: 375242