package.h: Update version number to 0.8.0
package.h: Update version number to 0.8.0

Per https://codereview.chromium.org/998653002/, we were going to call
the Windows client milestone 0.8.0. Now that the Crashpad client has
successfully shipped in a Chrome Windows canary, I think we can say that
we’re there. Or here.

Congratulations!

R=scottmg@chromium.org

Review URL: https://codereview.chromium.org/1484013004 .

chromium/crashpad,atom/crashpad,atom/crashpad,chromium/crashpad,atom/crashpad,chromium/crashpad