Multiple Packages Should Be Added to libspring-java Build-Depends

[殷啟聰]

Hi pkg-java team,

I am testing the new gradle_1.12-1 by building all its build-rdeps and
when I was building libspring-java in a clean Debian Sid, it showed
the following error:

```
FAILURE: Build failed with an exception.

* What went wrong:
Could not resolve all dependencies for configuration ':spring-context:compile'.
> Could not resolve org.jruby.ext.posix:jnr-posix:debian.
  Required by:
      org.springframework:spring-context:3.2.13.RELEASE > org.jruby:jruby:debian
   > No cached version of org.jruby.ext.posix:jnr-posix:debian
available for offline mode.
> Could not resolve com.github.jnr:jnr-constants:debian.
  Required by:
      org.springframework:spring-context:3.2.13.RELEASE > org.jruby:jruby:debian
   > No cached version of com.github.jnr:jnr-constants:debian
available for offline mode.
> Could not resolve org.jruby.extras:jffi:debian.
  Required by:
      org.springframework:spring-context:3.2.13.RELEASE > org.jruby:jruby:debian
   > No cached version of org.jruby.extras:jffi:debian available for
offline mode.
> Could not resolve org.jruby.extras:jaffl:debian.
  Required by:
      org.springframework:spring-context:3.2.13.RELEASE > org.jruby:jruby:debian
   > No cached version of org.jruby.extras:jaffl:debian available for
offline mode.
```

Clearly jnr-posix, jnr-constants, jffi and jaffl should be added to
Build-Depends. I guess they are in the Recommends section of the other
Build-Depends packages, and my Debian disabled installing the
Recommended packages, hence my environment is different to the
maintainers'.

Cheers,
Kai-Chung

-- 
/*
* 殷啟聰 | Kai-Chung Yan
* Full-time student of Providence University of Taiwan
* LinkedIn: <https://linkedin.com/in/seamlik>
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*/