Update to latest brightray

* vendor/brightray a4983ae...fdc5a74 (5):
  > Update to Chromium r202921
  > Pull in libchromiumcontent's Windows test support
  > Use the user-visible version number in our user agent string
  > Set the user agent string correctly on Windows
  > Automatically exclude platform-specific files for all targets
Fix crash on launch on Windows

We need to define a version so we can set up our user agent.
Merge pull request #12 from brightray/chromium-r202921

Update to latest brightray and Chromium r202921