fpm-1.11.0 cannot install on RHEL7 derived distro that use ruby2.0

[jsolomon8080]

The problem is (I think) that fpm dependency specification is too loose. It allows the latest ffi and git gem dependencies while when actually trying to install the latest version of these dependencies, they fail because those gems rely on ruby 2.3 and RHEL7 based distros use ruby2.0.

On a fresh CentOS7 AWS instance:

LSB Version:    :core-4.1-amd64:core-4.1-noarch
Distributor ID: CentOS
Description:    CentOS Linux release 7.9.2009 (Core)
Release:        7.9.2009
Codename:       Core
$ ruby -v
ruby 2.0.0p648 (2015-12-16) [x86_64-linux]

And this happens:

Fetching: cabin-0.9.0.gem (100%)
Successfully installed cabin-0.9.0
Fetching: backports-3.20.1.gem (100%)
Successfully installed backports-3.20.1
Fetching: arr-pm-0.0.10.gem (100%)
Successfully installed arr-pm-0.0.10
Fetching: clamp-1.0.1.gem (100%)
Successfully installed clamp-1.0.1
Fetching: ffi-1.14.2.gem (100%)
ERROR:  Error installing fpm:
        ffi requires Ruby version >= 2.3.

The workaround is:

gem install --version 1.12.2 --user-install ffi
gem install --version 1.6.0 --user-install git

So that fpm uses older versions of gems instead of the latest versions that rely on ruby 2.3.

I think a better solution is to detect ruby 2.0 and then constrain the ruby gem dependency versions to supported version.