[UPGRADE] Spark 2.9.3 -> 2.9.4

[chibenwa]

Fixes Jetty dependency management mess

[Arsnael]

Guess you went a bit fast on that one:

03:13:11,559 [ERROR] [ERROR] Some problems were encountered while processing the POMs:
[ERROR] 'dependencies.dependency.version' for org.eclipse.jetty:jetty-server:jar is missing. @ line 105, column 21
[ERROR] 'dependencies.dependency.version' for org.eclipse.jetty:jetty-server:jar is missing. @ line 167, column 21
[WARNING] 'dependencies.dependency.(groupId:artifactId:type:classifier)' must be unique: org.mockito:mockito-core:jar -> duplicate declaration of version (?) @ line 153, column 21
 @ 
03:13:11,561 [ERROR] The build could not read 2 projects -> [Help 1]
org.apache.maven.project.ProjectBuildingException: Some problems were encountered while processing the POMs:
[ERROR] 'dependencies.dependency.version' for org.eclipse.jetty:jetty-server:jar is missing. @ line 105, column 21
[ERROR] 'dependencies.dependency.version' for org.eclipse.jetty:jetty-server:jar is missing. @ line 167, column 21
[WARNING] 'dependencies.dependency.(groupId:artifactId:type:classifier)' must be unique: org.mockito:mockito-core:jar -> duplicate declaration of version (?) @ line 153, column 21