histogram support for ruby client

[rolandhawk]

Is this acceptable?

ref #21

[coveralls]

Coverage decreased (-0.1%) to 99.589% when pulling 723890a on bukalapak:master into 670c45c on prometheus:master.

[brian-brazil]

You must expose a +Inf bucket wit the same value as _count

[coveralls]

Coverage increased (+0.03%) to 99.728% when pulling 8a02940 on bukalapak:master into 670c45c on prometheus:master.

[coveralls]

Coverage increased (+0.03%) to 99.729% when pulling ae0af38 on bukalapak:master into 670c45c on prometheus:master.

[brian-brazil]

This should be called observe

[grobie]

Thanks for your contribution! This looks great in general, please only fix the last few comments.

I updated the formatting to the latest rubocop rules (not sure following rubocop was a good idea, they change their mind so often ...). Please rebase and squash your changes against current master. I'll fix the test dependencies for "old" ruby versions tomorrow.

[rolandhawk]

Hi @grobie @brian-brazil, I have updated my PR, please kindly check it

[coveralls]

Coverage increased (+0.04%) to 99.733% when pulling f4a4ea9 on bukalapak:master into 58bd969 on prometheus:master.

[grobie]

Thanks a lot @rolandhawk!