Removing invalid "RUBY_VERSION" Ruby version string from Gemfile

[AndrewRayCode]

The Gemfile specifies the exact required ruby version as "RUBY_VERSION"
which is not a ruby version. Unless there's some hidden Ruby version
requirement of this Gem, I don't see a point in keeping it?

This is the warning RVM spits out for every Terminal action:

RVM used your Gemfile for selecting Ruby, it is all fine - Heroku does that too,
you can ignore these warnings with 'rvm rvmrc warning ignore fhir_client/Gemfile'.
To ignore the warning for all files run 'rvm rvmrc warning ignore allGemfiles'.

Unknown ruby interpreter version (do not know how to handle): RUBY_VERSION.

[olbrich]

@AndrewRayCode older versions of bundler did not set the ruby version requirement for gems to the currently executing ruby VM, so you could get into weird situations with dependencies when using old versions of ruby. Bundler would update dependencies to ones that weren't compatible with the version you were running. This hack sets the required ruby version to the version of the current interpreter (as defined by the RUBY_VERSION constant).

I don't think this is required anymore, but that's why it was there.

[AndrewRayCode]

@olbrich interesting. I don't know enough about the ruby ecosystem to make a call here, just noticed that I got a big warning every time I hit enter in my shell

[arscan]

I'll go ahead and merge this PR, if it is a workaround that isn't required any more. Thanks @AndrewRayCode and @olbrich