Psych 3.1 is required since we assert safe_load accepts kwargs

Followup to discussion in ManageIQ/manageiq-appliance_console#234

3.1 safe_load changed positional to kwargs like aliases: true: ruby/psych@4d4439d

Note, there are other changes to psych over time that ease the changes to the psych 4 defaults to safe_load
but this is the absolute minimum we need.

safe_load_file was added in 3.2.1:
ruby/psych@0210e31

unsafe_load and unsafe_load_file was added in 3.3.2:
ruby/psych@cb50aa8

safe_load was added with positional arguments in 2.0.0:
ruby/psych@2c644e1

Gemfile

@@ -61,6 +61,7 @@ gem "net-ldap",                         "~>0.16.1",          :require => false
 gem "net-ping",                         "~>1.7.4",           :require => false
 gem "openscap",                         "~>0.4.8",           :require => false
 gem "optimist",                         "~>3.0",             :require => false
+gem "psych",                            ">=3.1",             :require => false # 3.1 safe_load changed positional to kwargs like aliases: true: https://github.com/ruby/psych/commit/4d4439d6d0adfcbd211ea295779315f1baa7dadd
 gem "pg",                               ">=1.4.1",           :require => false
 gem "pg-dsn_parser",                    "~>0.1.1",           :require => false
 gem "query_relation",                   "~>0.1.0",           :require => false