ruby: bump to 2.6.1

ruby: bump to 2.6.1

See: https://www.ruby-lang.org/en/news/2019/01/30/ruby-2-6-1-released/
See: https://www.ruby-lang.org/en/news/2018/12/25/ruby-2-6-0-released/

New packages mirroring upstream gemification of ruby:
* ruby-bundler (new)
* ruby-e2mmap and ruby-ostruct (from ruby-misc)
* ruby-forwardable (from ruby-patterns)
* ruby-matrix and ruby-prime (from removed ruby-math)
* ruby-mutex_m, ruby-sync and ruby-thwait (from ruby-multithread)
* ruby-tracer (from ruby-debuglib)

Added ruby-dev for building extension inside openwrt (requires cc)

Signed-off-by: Luiz Angelo Daros de Luca <redacted>