Pass resolved instance location to custom keywords

Never meant to expose `Location` hashes. Looks like this was an
oversight when they were introduced.

Noticed this while looking into: #166

lib/json_schemer/schema.rb

@@ -149,9 +149,10 @@ def validate_instance(instance, instance_location, keyword_location, context)
         end
 
         if root.custom_keywords.any?
+          resolved_instance_location = Location.resolve(instance_location)
           root.custom_keywords.each do |custom_keyword, callable|
             if value.key?(custom_keyword)
-              [*callable.call(instance, value, instance_location)].each do |custom_keyword_result|
+              [*callable.call(instance, value, resolved_instance_location)].each do |custom_keyword_result|
                 custom_keyword_valid = custom_keyword_result == true
                 valid &&= custom_keyword_valid
                 type = custom_keyword_result.is_a?(String) ? custom_keyword_result : custom_keyword

test/json_schemer_test.rb

@@ -228,6 +228,32 @@ def test_it_validates_custom_keywords_in_nested_schemas
     refute(schemer.valid?({ 'x' => 'invalid' }))
   end
 
+  def test_custom_keywords_receive_resolved_instance_location
+    custom_keyword_instance_location = nil
+    schemer = JSONSchemer.schema(
+      {
+        'properties' => {
+          'x' => {
+            'yah' => true
+          },
+          'y' => {
+            'yah' => true
+          }
+        }
+      },
+      keywords: {
+        'yah' => proc do |instance, _schema, instance_location|
+          custom_keyword_instance_location = instance_location
+          instance == 'valid'
+        end
+      }
+    )
+    assert(schemer.valid?({ 'x' => 'valid' }))
+    assert_equal('/x', custom_keyword_instance_location)
+    refute(schemer.valid?({ 'y' => 'invalid' }))
+    assert_equal('/y', custom_keyword_instance_location)
+  end
+
   def test_it_handles_multiple_of_floats
     assert(JSONSchemer.schema({ 'multipleOf' => 0.01 }).valid?(8.61))
     refute(JSONSchemer.schema({ 'multipleOf' => 0.01 }).valid?(8.666))