Check local portion of email for invalid dots

Addresses failures related to: json-schema-org/JSON-Schema-Test-Suite#405

Author: davishmcclurg

lib/json_schemer/format.rb

@@ -70,7 +70,9 @@ def valid_date_time?(data)
     end
 
     def valid_email?(data)
-      EMAIL_REGEX.match?(data)
+      return false unless EMAIL_REGEX.match?(data)
+      local, _domain = data.partition('@')
+      !local.start_with?('.') && !local.end_with?('.') && !local.include?('..')
     end
 
     def valid_hostname?(data)