update year on debian copyright

debian/copyright

@@ -3,7 +3,7 @@ Upstream-Name: step-certificates
 Source: https://github.com/smallstep/certificates
 
 Files: *
-Copyright: 2019 Smallstep Labs, Inc.
+Copyright: 2020 Smallstep Labs, Inc.
 License: Apache 2.0
 
 License: Apache 2.0
@@ -19,4 +19,4 @@ License: Apache 2.0
  distributed under the License is distributed on an "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing permissions and
- limitations under the License.
+ limitations under the License.