Use ruby/net-smtp#90

Author: hsbt

gems/bundled_gems

@@ -15,7 +15,7 @@ rss                 0.3.1   https://github.com/ruby/rss
 net-ftp             0.3.8   https://github.com/ruby/net-ftp
 net-imap            0.5.5   https://github.com/ruby/net-imap
 net-pop             0.1.2   https://github.com/ruby/net-pop
-net-smtp            0.5.0   https://github.com/ruby/net-smtp
+net-smtp            0.5.0   https://github.com/ruby/net-smtp d496a829f9b99adb44ecc1768c4d005e5f7b779e
 matrix              0.4.2   https://github.com/ruby/matrix
 prime               0.1.3   https://github.com/ruby/prime
 rbs                 3.8.1   https://github.com/ruby/rbs