bumped version to 2.4.1 and fixed backwards incompatible behaviour

[mburger]

as was brought to my attention today, it seems my last pull request broke the default behaviour when specifying ssl => true, as we now pass a string and march-hare does not validate what you pass to it and just assumes its the name of a valid securiry context, i'm truly sorry for the trouble this might have caused already but as i didnt use a boolean value in the config myself and the tests where green i assumed the change will be ok, this pull request fixes it

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Error Message:
{:timestamp=>"2016-05-03T07:42:21.273000+0000", :message=>"true SSLContext not available", :class=>"Java::JavaSecurity::NoSuchAlgorithmException", :location=>"sun.security.jca.GetInstance.getInstance(sun/security/jca/GetInstance.java:159)", :level=>:warn, :file=>"logstash/inputs/rabbitmq.rb", :line=>"180", :method=>"register"}

[andrewvc]

Thanks for the PR @mburger . I think my PR #22 will do a more complete job. I'm going to close this one given that I plan on merging that soon.

WDYT?

[mburger]

@andrewvc sounds good :)