Update prebuild to 6.0.0
Update prebuild to 6.0.0

Updating prebuild should fix the installation with yarn https://github.com/mafintosh/prebuild/issues/132

Change-Id: I642950c9661eca285ecc522d999d5fcc999a9ca5
Reviewed-on: http://review.couchbase.org/72943
Reviewed-by: Brett Lawson <c8c4369773d7d7226e031f0c4af62e3f38a08510@gmail.com>
Tested-by: Brett Lawson <c8c4369773d7d7226e031f0c4af62e3f38a08510@gmail.com>

brett19/couchnode,couchbase/couchnode,couchbase/couchnode,couchbase/couchnode,couchbase/couchnode,brett19/couchnode,brett19/couchnode