Fixed typo in documentation

README.md

@@ -294,7 +294,7 @@ The most recent email:
 ```ruby
 Mail.all    #=> Returns an array of all emails
 Mail.first  #=> Returns the first unread email
-Mail.last   #=> Returns the first unread email
+Mail.last   #=> Returns the last unread email
 ```
 
 The first 10 emails sorted by date in ascending order:

lib/mail/network/retriever_methods/imap.rb

@@ -18,7 +18,7 @@ module Mail
   #
   #   Mail.all    #=> Returns an array of all emails
   #   Mail.first  #=> Returns the first unread email
-  #   Mail.last   #=> Returns the first unread email
+  #   Mail.last   #=> Returns the last unread email
   #
   # You can also pass options into Mail.find to locate an email in your imap mailbox
   # with the following options:

lib/mail/network/retriever_methods/pop3.rb

@@ -18,7 +18,7 @@ module Mail
   # 
   #   Mail.all    #=> Returns an array of all emails
   #   Mail.first  #=> Returns the first unread email
-  #   Mail.last   #=> Returns the first unread email
+  #   Mail.last   #=> Returns the last unread email
   # 
   # You can also pass options into Mail.find to locate an email in your pop mailbox
   # with the following options: