Relaxed json runtime dependency breaks Ruby 1.9. compatibility

[petetnt]

The README.md states that

Tested with Ruby 1.9, 2.0, 2.1, 2.2 and 2.3.

However, installing gelf on 1.9. leads to

gem install gelf
ERROR:  Error installing gelf:
    json requires Ruby version ~> 2.0.

The runtime_dependency is added as

s.add_runtime_dependency(%q<json>, [">= 0"])

So I assume that json had a breaking change somewhere which then breaks gelf-rb.

[milgner]

That is strange, the tests on Travis CI were all running successfully. Nonetheless, I have just published a new version to the master branch, could you give it a try? It should use json 1.8.3, which still supports older Rubies. Let me know if it does not work and I will add an explicit version restriction.