Update copyright to 2020.

LICENSE

src/main/java/org/torproject/metrics/collector/Main.java

.../metrics/collector/bridgedb/BridgedbMetricsProcessor.java

...metrics/collector/bridgedescs/BridgeDescriptorParser.java

...t/metrics/collector/bridgedescs/BridgeSnapshotReader.java

...ject/metrics/collector/bridgedescs/DescriptorBuilder.java

...metrics/collector/bridgedescs/SanitizedBridgesWriter.java

...collector/bridgepools/BridgePoolAssignmentsProcessor.java

...ava/org/torproject/metrics/collector/conf/Annotation.java

.../org/torproject/metrics/collector/conf/Configuration.java

...roject/metrics/collector/conf/ConfigurationException.java

src/main/java/org/torproject/metrics/collector/conf/Key.java

...ava/org/torproject/metrics/collector/conf/SourceType.java

.../org/torproject/metrics/collector/cron/CollecTorMain.java

...java/org/torproject/metrics/collector/cron/Scheduler.java

...a/org/torproject/metrics/collector/cron/ShutdownHook.java

...g/torproject/metrics/collector/downloader/Downloader.java

...oject/metrics/collector/exitlists/ExitListDownloader.java

...torproject/metrics/collector/indexer/CreateIndexJson.java

...g/torproject/metrics/collector/indexer/DirectoryNode.java