fix sbt-projectmatrix mixing dependency

[arnaud-daroussin]

Hi @novakov-alexey,

sbt-projectmatrix is quite new for me, so its usage is still uncertain. But it should to do the trick to fix the dependency issue in #320.

Actually, it seems logical. flink-1-api and flink-2-api projects were referencing flink (-common) project but nothing was telling them to pick Flink1 or Flink2 variations of this project, so both were picking arbitrarily the first variation Flink1.

The fix consists to specify the correct "Flink" axis to both sub-project in addition to JVM axis.

Now each project is picking the correct parent dependency. I checked all produced pom and they are good.

And by tweaking FlinkAxis a bit more, I'm able to keep a "fair enough" project IDs naming:

sbt projects
[info]     docs
[info]     docs3
[info]     examples3
[info]     flink-1-api
[info]     flink-1-api-common
[info]     flink-1-api-common3
[info]     flink-1-api3
[info]     flink-2-api
[info]     flink-2-api-common
[info]     flink-2-api-common3
[info]     flink-2-api3
[info]   * flink-scala-api

[novakov-alexey]

Thanks for the PR.