[Scala] Fix missing dependencies in Scala API client pom.xml

[ePaul]

PR checklist

• Read the contribution guidelines.
• Ran the shell/batch script under ./bin/ to update Petstore sample so that CIs can verify the change.
  → bin/scala-petstore.sh
• Filed the PR against the correct branch: master for non-breaking changes and 2.3.0 branch for breaking (non-backward compatible) changes.

Description of the PR

I noticed that my merge of master and 2.3.0 had a different version number than both master and 2.3.0.
The reason is that the master sample was not up-to-date (#4881 forgot to update the scala samples).

[ePaul]

As predicted, Travis breaks:

INFO] --- scala-maven-plugin:3.1.5:compile (scala-compile-first) @ swagger-scala-client ---
[INFO] /home/travis/build/swagger-api/swagger-codegen/samples/client/petstore/scala/src/main/scala:-1: info: compiling
[INFO] Compiling 10 source files to /home/travis/build/swagger-api/swagger-codegen/samples/client/petstore/scala/target/classes at 1489682820931
[ERROR] /home/travis/build/swagger-api/swagger-codegen/samples/client/petstore/scala/src/main/scala/io/swagger/client/ApiInvoker.scala:34: error: object datatype is not a member of package com.fasterxml.jackson
[ERROR] import com.fasterxml.jackson.datatype.joda.JodaModule
[ERROR]                              ^
[ERROR] /home/travis/build/swagger-api/swagger-codegen/samples/client/petstore/scala/src/main/scala/io/swagger/client/ApiInvoker.scala:44: error: not found: type JodaModule
[ERROR]     mapper.registerModule(new JodaModule());
[ERROR]                               ^
[ERROR] two errors found

I'll add the missing dependency directly to the pom.mustache.