Add date format to OpenAPI 3.0

This shouldn't've been removed in: ccffac7
I was under the impression that it would be provided by draft4 since
that's openapi30's meta schema, but it's not in that spec.

OpenAPI 3.0 formats listed here: https://spec.openapis.org/oas/v3.0.3#data-types

@ahx noticed this here: #149 (comment)

Author: davishmcclurg

lib/json_schemer/openapi30/meta.rb

@@ -5,7 +5,8 @@ module OpenAPI30
     # https://spec.openapis.org/oas/v3.0.3#data-types
     FORMATS = OpenAPI31::FORMATS.merge(
       'byte' => proc { |instance, _value| Format.decode_content_encoding(instance, 'base64').first },
-      'binary' => proc { |instance, _value| instance.is_a?(String) && instance.encoding == Encoding::ASCII_8BIT }
+      'binary' => proc { |instance, _value| instance.is_a?(String) && instance.encoding == Encoding::ASCII_8BIT },
+      'date' => Format::DATE
     )
     SCHEMA = {
       'id' => 'json-schemer://openapi30/schema',

test/open_api_test.rb

@@ -735,7 +735,9 @@ def test_openapi30_formats
         'd' => { 'format' => 'double' },
         'e' => { 'format' => 'password' },
         'f' => { 'format' => 'byte' },
-        'g' => { 'format' => 'binary' }
+        'g' => { 'format' => 'binary' },
+        'h' => { 'format' => 'date' },
+        'i' => { 'format' => 'date-time' }
       }
     }
 
@@ -756,6 +758,10 @@ def test_openapi30_formats
     assert(schemer.valid?({ 'f' => 'IQ==' }))
     refute(schemer.valid?({ 'g' => '!' }))
     assert(schemer.valid?({ 'g' => '!'.b }))
+    refute(schemer.valid?({ 'h' => '2001-02-03T04:05:06.123456789+07:00' }))
+    assert(schemer.valid?({ 'h' => '2001-02-03' }))
+    refute(schemer.valid?({ 'i' => '2001-02-03' }))
+    assert(schemer.valid?({ 'i' => '2001-02-03T04:05:06.123456789+07:00' }))
   end
 
   def test_unsupported_openapi_version