Fix a couple typos (#590)

lib/restclient.rb

@@ -39,7 +39,7 @@ require File.dirname(__FILE__) + '/restclient/windows'
 #   # DELETE
 #   RestClient.delete 'http://example.com/resource'
 #
-#   # retreive the response http code and headers
+#   # retrieve the response http code and headers
 #   res = RestClient.get 'http://example.com/some.jpg'
 #   res.code                    # => 200
 #   res.headers[:content_type]  # => 'image/jpg'

lib/restclient/raw_response.rb

@@ -1,7 +1,7 @@
 module RestClient
   # The response from RestClient on a raw request looks like a string, but is
   # actually one of these.  99% of the time you're making a rest call all you
-  # care about is the body, but on the occassion you want to fetch the
+  # care about is the body, but on the occasion you want to fetch the
   # headers you can:
   #
   #   RestClient.get('http://example.com').headers[:content_type]