Update copyright dates for 2019

Happy new year! Bumping the dates for 2019...

  % find . -type f -iname '*.py' -exec sed -i 's/-2018/-2019/g' "{}" +;
  % grep -R "# Copyright 2018," ./*

consensus_health_checker.py

 #!/usr/bin/env python
-# Copyright 2013-2017, Damian Johnson and The Tor Project
+# Copyright 2013-2019, Damian Johnson and The Tor Project
 # See LICENSE for licensing information
 
 """

descriptor_checker.py

 #!/usr/bin/env python
-# Copyright 2013-2017, Damian Johnson and The Tor Project
+# Copyright 2013-2019, Damian Johnson and The Tor Project
 # See LICENSE for licensing information
 
 """

fallback_directories.py

 #!/usr/bin/env python
-# Copyright 2016-2017, Damian Johnson and The Tor Project
+# Copyright 2016-2019, Damian Johnson and The Tor Project
 # See LICENSE for licensing information
 
 """

fingerprint_change_checker.py

 #!/usr/bin/env python
-# Copyright 2015-2017, Damian Johnson and The Tor Project
+# Copyright 2015-2019, Damian Johnson and The Tor Project
 # See LICENSE for licensing information
 
 """

package_versions.py

 #!/usr/bin/env python
-# Copyright 2017, Damian Johnson and The Tor Project
+# Copyright 2017-2019, Damian Johnson and The Tor Project
 # See LICENSE for licensing information
 
 """

relay_check.py

 #!/usr/bin/env python
-# Copyright 2018, Damian Johnson and The Tor Project
+# Copyright 2018-2019, Damian Johnson and The Tor Project
 # See LICENSE for licensing information
 
 """

sybil_checker.py

 #!/usr/bin/env python
-# Copyright 2013-2017, Damian Johnson and The Tor Project
+# Copyright 2013-2019, Damian Johnson and The Tor Project
 # See LICENSE for licensing information
 
 """

track_relays.py

 #!/usr/bin/env python
-# Copyright 2016-2017, Damian Johnson and The Tor Project
+# Copyright 2016-2019, Damian Johnson and The Tor Project
 # See LICENSE for licensing information
 
 """