Pin ffi version

Gemfile

@@ -12,7 +12,7 @@ ruby_version_segments = ruby_version.segments
 minor_version = ruby_version_segments[0..1].join('.')
 
 group :development do
-  gem "ffi", "= 1.16.3"                                           # https://github.com/ffi/ffi/issues/1103
+  gem "ffi", "= 1.16.3"                                            if ruby_version >= Gem::Version.new('2.5') # https://github.com/ffi/ffi/issues/1103 (pin only for Ruby >= 2.5 as this version is not compatible below. ffi 1.17 is not compatible with Ruby 2.5: https://github.com/ffi/ffi/issues/1103)
   gem "rake", "~> 12.3.3"                                          if ruby_version < Gem::Version.new('2.6.0') # last version for ruby < 2.6
   gem "semantic_puppet", '= 1.0.4'
   gem "xmlrpc"                                                      if ruby_version >= Gem::Version.new('2.3')