Use ruby/net-imap#389 for flaky tests

Author: hsbt

gems/bundled_gems

@@ -13,7 +13,7 @@ test-unit           3.6.7   https://github.com/test-unit/test-unit
 rexml               3.4.0   https://github.com/ruby/rexml
 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-imap            0.5.5   https://github.com/ruby/net-imap 29aa826936c977c6ddc8183cca355b0eb65b5529
 net-pop             0.1.2   https://github.com/ruby/net-pop
 net-smtp            0.5.0   https://github.com/ruby/net-smtp d496a829f9b99adb44ecc1768c4d005e5f7b779e
 matrix              0.4.2   https://github.com/ruby/matrix