upgrade to cassandra 2.0.8 in travis test

they removed 2.0.7 from the repo
Separate metadata and agent_checks synchronization
Merge branch 'fix_proxy' into v4.x
Merge branch 'v4.3.1' into v4.x
Merge branch 'master' into v4.x
Merge branch 'master' into v4.x
Merge branch 'fix_proxy' into v4.x
Merge branch 'master' into v4.x
Merge branch 'master' into v4.x
Merge branch 'master' into v4.x
Merge branch 'master' into v4.x
Merge branch 'master' into v4.x
Merge branch 'master' into v4.x
Merge branch 'v4.3.1'
Merge branch 'master' into v4.x
Merge pull request #993 from DataDog/v4.3.1

Separate metadata and agent_checks synchronization
Merge branch 'master' into v4.x
Update CHANGELOG.md
Add support for optional message with service checks.
Merge pull request #995 from DataDog/conor/service-check-message

Add support for optional message with service checks.