Don't run Rails 5.0+ appraisals on Ruby < 2.2.2

They're excluded in the Travis matrix but for convenience also prevent
them from running when using the `rake appraisals` command.

Author: pixeltrix

Appraisals

@@ -4,14 +4,16 @@ appraise "rails-4-2" do
   gem "activemodel", "~> 4.2.0"
 end
 
-appraise "rails-5-0" do
-  gem "railties",    "~> 5.0.0"
-  gem "actionpack",  "~> 5.0.0"
-  gem "activemodel", "~> 5.0.0"
-end
+if RUBY_VERSION >= "2.2.2"
+  appraise "rails-5-0" do
+    gem "railties",    "~> 5.0.0"
+    gem "actionpack",  "~> 5.0.0"
+    gem "activemodel", "~> 5.0.0"
+  end
 
-appraise "rails-5-1" do
-  gem "railties",    ">= 5.1.0", "< 5.2"
-  gem "actionpack",  ">= 5.1.0", "< 5.2"
-  gem "activemodel", ">= 5.1.0", "< 5.2"
+  appraise "rails-5-1" do
+    gem "railties",    ">= 5.1.0", "< 5.2"
+    gem "actionpack",  ">= 5.1.0", "< 5.2"
+    gem "activemodel", ">= 5.1.0", "< 5.2"
+  end
 end