fix: add missing javax.annotation dependency to pom.xml

[dancesWithCycles]

Hi folks,
Thank you very much for providing and maintaining this repository.

Calling mvn clean package on the master branch came back with the following reply.

[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  2.411 s
[INFO] Finished at: 2022-09-06T12:56:16+02:00
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.8.0:compile (default-compile) on project onebusaway-gtfs-realtime-exporter: Compilation failure: Compilation failure: 
[ERROR] /home/begerad/git/dancesWithCycles/onebusaway-gtfs-realtime-exporter/src/main/java/org/onebusaway/gtfs_realtime/exporter/GtfsRealtimeFileWriter.java:[27,24] package javax.annotation does not exist
[ERROR] /home/begerad/git/dancesWithCycles/onebusaway-gtfs-realtime-exporter/src/main/java/org/onebusaway/gtfs_realtime/exporter/GtfsRealtimeFileWriter.java:[28,24] package javax.annotation does not exist
[ERROR] /home/begerad/git/dancesWithCycles/onebusaway-gtfs-realtime-exporter/src/main/java/org/onebusaway/gtfs_realtime/exporter/GtfsRealtimeFileWriter.java:[83,4] cannot find symbol
[ERROR]   symbol:   class PostConstruct
[ERROR]   location: class org.onebusaway.gtfs_realtime.exporter.GtfsRealtimeFileWriter
[ERROR] /home/begerad/git/dancesWithCycles/onebusaway-gtfs-realtime-exporter/src/main/java/org/onebusaway/gtfs_realtime/exporter/GtfsRealtimeFileWriter.java:[89,4] cannot find symbol
[ERROR]   symbol:   class PreDestroy
[ERROR]   location: class org.onebusaway.gtfs_realtime.exporter.GtfsRealtimeFileWriter
[ERROR] -> [Help 1]
[ERROR] 
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR] 
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoFailureException

That is why I added this dependency. How could you run this repository in the past without this dependency in the pom.xml file?

Only this patch makes me able to get a BUILD SUCCESS.

Please feel free to study, use, share or change this pull request.

Cheers!

[CLAassistant]

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