Add missing punctuation mark to all ActionMailer docs [ci skip]

actionmailer/lib/action_mailer/gem_version.rb

 module ActionMailer
-  # Returns the version of the currently loaded Action Mailer as a <tt>Gem::Version</tt>
+  # Returns the version of the currently loaded Action Mailer as a <tt>Gem::Version</tt>.
   def self.gem_version
     Gem::Version.new VERSION::STRING
   end

actionmailer/lib/action_mailer/log_subscriber.rb

@@ -29,7 +29,7 @@ def process(event)
       end
     end
 
-    # Use the logger configured for ActionMailer::Base
+    # Use the logger configured for ActionMailer::Base.
     def logger
       ActionMailer::Base.logger
     end

actionmailer/lib/action_mailer/message_delivery.rb

@@ -60,9 +60,9 @@ def deliver_later!(options={})
     #
     # Options:
     #
-    # * <tt>:wait</tt> - Enqueue the email to be delivered with a delay
-    # * <tt>:wait_until</tt> - Enqueue the email to be delivered at (after) a specific date / time
-    # * <tt>:queue</tt> - Enqueue the email on the specified queue
+    # * <tt>:wait</tt> - Enqueue the email to be delivered with a delay.
+    # * <tt>:wait_until</tt> - Enqueue the email to be delivered at (after) a specific date / time.
+    # * <tt>:queue</tt> - Enqueue the email on the specified queue.
     def deliver_later(options={})
       enqueue_delivery :deliver_now, options
     end

actionmailer/lib/action_mailer/preview.rb

@@ -52,7 +52,7 @@ class Preview
     extend ActiveSupport::DescendantsTracker
 
     class << self
-      # Returns all mailer preview classes
+      # Returns all mailer preview classes.
       def all
         load_previews if descendants.empty?
         descendants
@@ -68,27 +68,27 @@ def call(email)
         message
       end
 
-      # Returns all of the available email previews
+      # Returns all of the available email previews.
       def emails
         public_instance_methods(false).map(&:to_s).sort
       end
 
-      # Returns true if the email exists
+      # Returns true if the email exists.
       def email_exists?(email)
         emails.include?(email)
       end
 
-      # Returns true if the preview exists
+      # Returns true if the preview exists.
       def exists?(preview)
         all.any?{ |p| p.preview_name == preview }
       end
 
-      # Find a mailer preview by its underscored class name
+      # Find a mailer preview by its underscored class name.
       def find(preview)
         all.find{ |p| p.preview_name == preview }
       end
 
-      # Returns the underscored name of the mailer preview without the suffix
+      # Returns the underscored name of the mailer preview without the suffix.
       def preview_name
         name.sub(/Preview$/, '').underscore
       end

actionmailer/lib/action_mailer/test_helper.rb

@@ -2,7 +2,7 @@
 
 module ActionMailer
   # Provides helper methods for testing Action Mailer, including #assert_emails
-  # and #assert_no_emails
+  # and #assert_no_emails.
   module TestHelper
     include ActiveJob::TestHelper