Increasing JDK baseline for "jackson-jr" from JDK 6 to JDK 8?

[Tatu Saloranta]

Given how long it has been since JDK 6 was supported, and that most
pre-JDK-9 usage has moved on to JDK 8, it seems reasonable to start
moving the last Jackson components to that baseline.
While I don't feel the need to change jackson-annotations or
jackson-core (streaming) at this point, "jackson-jr" looks like that
could benefit from upgrade -- there is now a request to support use of
"@Transient" -- but even aside from that, I wonder if there is any
reason to explicitly to support version of JDK on which project does
not build any more.

Move could occur for Jackson 2.14(.0), tentatively.

So: if you do use jackson-jr on Java 6 or Java 7 (or know some users),
please let me know!

-+ Tatu +-