Only install license_finder on modern Rubies

Reasons:
- The latest license_finder requires 2.3
- We don't need to run license_finder on all Rubies, just one is enough
  for the Travis builds
- Running license_finder is not part of the day-to-day development
  process, so not having it available is not a problem.

Gemfile

@@ -28,6 +28,7 @@ group :debug do
   end
 end
 
+# Tools to run during development
 group :development do
   # Needed for lint:yard:junk task
   if RUBY_VERSION >= '2.3.0'
@@ -76,17 +77,10 @@ group :development, :test do
   # gem 'cucumber-pro', '~> 0.0'
 
   # License compliance
-  if RUBY_VERSION < '2.3'
-    gem 'license_finder', '~> 2.0'
-  else
+  if RUBY_VERSION >= '2.3'
     gem 'license_finder', '~> 5.0'
   end
 
-  # Force compatible version of httparty for use by license_finder
-  if RUBY_VERSION <= '2.0.0'
-    gem 'httparty', '0.14.0'
-  end
-
   # Upload documentation
   # gem 'relish', '~> 0.7.1'
 

Rakefile

@@ -57,7 +57,11 @@ namespace :lint do
 
   desc 'Check for relevant licenses in project'
   task :licenses do
-    sh 'bundle exec license_finder'
+    if RUBY_VERSION >= '2.3'
+      sh 'bundle exec license_finder'
+    else
+      warn 'Your ruby version is not supported for license checking'
+    end
   end
 
   begin