downgrade jackson-databind to match version used in spark and aws-sdk

spark uses 2.6.7.1, and aws-java-sdk-s3 uses 2.6.7.3. There are no conflicts between the two, so we can explicitly use the latter.

When running spark with the newer version of jackson-databind (2.10.2), it produces the following runtime error:

Exception in thread "main" java.lang.ExceptionInInitializerError
	at org.apache.spark.SparkContext.withScope(SparkContext.scala:693)
	at org.apache.spark.SparkContext.parallelize(SparkContext.scala:710)
	at org.apache.spark.api.java.JavaSparkContext.parallelize(JavaSparkContext.scala:134)
	at org.janelia.stitching.PipelineFusionStepExecutor.fuse(PipelineFusionStepExecutor.java:276)
	at org.janelia.stitching.PipelineFusionStepExecutor.runImpl(PipelineFusionStepExecutor.java:179)
	at org.janelia.stitching.PipelineFusionStepExecutor.run(PipelineFusionStepExecutor.java:69)
	at org.janelia.stitching.StitchingSpark.run(StitchingSpark.java:87)
	at org.janelia.stitching.StitchingSpark.main(StitchingSpark.java:34)
Caused by: com.fasterxml.jackson.databind.JsonMappingException: Incompatible Jackson version: 2.10.2
	at com.fasterxml.jackson.module.scala.JacksonModule$class.setupModule(JacksonModule.scala:64)
	at com.fasterxml.jackson.module.scala.DefaultScalaModule.setupModule(DefaultScalaModule.scala:19)
	at com.fasterxml.jackson.databind.ObjectMapper.registerModule(ObjectMapper.java:808)
	at org.apache.spark.rdd.RDDOperationScope$.<init>(RDDOperationScope.scala:82)
	at org.apache.spark.rdd.RDDOperationScope$.<clinit>(RDDOperationScope.scala)
	... 8 more

Author: Igor Pisarev

pom.xml

@@ -872,7 +872,7 @@
 		<jackrabbit-webdav.version>2.21.0</jackrabbit-webdav.version>
 
 		<!-- Jackson - https://github.com/FasterXML/jackson -->
-		<jackson-databind.version>2.10.2</jackson-databind.version>
+		<jackson-databind.version>2.6.7.3</jackson-databind.version>
 
 		<!-- Java Advanced Imaging - https://java.net/projects/jai-core -->
 		<jai.version>1.1.3</jai.version>