Installation failed with logstash 6.2+

[sc0rp10]

Hi!
I can not install version 0.1.0 of logstash-output-clickhouse because of failed dependencies:
`` `
$ bin / logstash-plugin install --local --no-verify /tmp/logstash-output-clickhouse-0.1.0.gem
Installing logstash-output-clickhouse
Plugin version conflict, aborting
ERROR: Installation Aborted, message: Bundler could not find compatible versions for gem "logstash-mixin-http_client":
  In snapshot (Gemfile.lock):
    logstash-mixin-http_client (= 6.0.0)

  In Gemfile:
    logstash-input-http_poller (> = 0) java depends on
      logstash-mixin-http_client (<7.0.0,> = 6.0.0) java

    logstash-input-http_poller (> = 0) java depends on
      logstash-mixin-http_client (<7.0.0,> = 6.0.0) java

    logstash-output-clickhouse (= 0.1.0) java depends on
      logstash-mixin-http_client (<6.0.0,> = 2.2.1) java

    logstash-mixin-http_client (= 6.0.0) java

Running bundle update will rebuild your snapshot from scratch, using only
the gems in your Gemfile, which may resolve the conflict.
`` `

So I can not downgrade logstash-mixin-http_client because of it will brake many of default plugins.

Can you please bump the version of logstash-mixin-http_client to the> = 6.0.0?

I can PR this change in gemspecs, but I'm not a ruby ​​developer and can not test this change.

[eddurov]

Made PR. Checked on "logstash.version"=>"7.1.1"