Fix Rubocop offenses (#92)

* Rubocop fix: Use filter_map instead of map { ... }.compact

Currently, builds are failing because of Rubocop complaining about these
three lines.

* Drop support for Ruby 2.6

Array#filter_map is only introduced in Ruby 2.7. This ensures we're
still supporting the 2.x series, but drops support for the now pretty
old Ruby 2.6.

Author: mamhoff

.github/workflows/ci.yml

@@ -8,10 +8,10 @@ jobs:
 
     strategy:
       matrix:
-        ruby: [2.6, '3.0', '3.1', 3.2]
+        ruby: [2.7, '3.0', '3.1', 3.2]
         rails: [6, 7]
         exclude:
-          - ruby: '2.6'
+          - ruby: '2.7'
             rails: 7
           - ruby: 3.2
             rails: 6

lib/jsonapi/deserialization.rb

@@ -65,7 +65,7 @@ def jsonapi_deserialize(document, options = {})
         rel_name = jsonapi_inflector.singularize(assoc_name)
 
         if assoc_data.is_a?(Array)
-          parsed["#{rel_name}_ids"] = assoc_data.map { |ri| ri['id'] }.compact
+          parsed["#{rel_name}_ids"] = assoc_data.filter_map { |ri| ri['id'] }
           next
         end
 

lib/jsonapi/fetching.rb

@@ -17,7 +17,7 @@ def jsonapi_fields
       end
 
       params[:fields].each do |k, v|
-        extracted[k] = v.to_s.split(',').map(&:strip).compact
+        extracted[k] = v.to_s.split(',').filter_map(&:strip)
       end
 
       extracted
@@ -29,7 +29,7 @@ def jsonapi_fields
     #
     # @return [Array]
     def jsonapi_include
-      params['include'].to_s.split(',').map(&:strip).compact
+      params['include'].to_s.split(',').filter_map(&:strip)
     end
   end
 end