CHANGELOG: mark 0.4.19 as unreleased

License: MIT
Signed-off-by: Steven Allen <steven@stebalien.com>

CHANGELOG.md

 # go-ipfs changelog
 
-## 0.4.19 2018-02-14
+## 0.4.19 2018-02-14 (unreleased)
 
 We're happy to announce go 0.4.19. As usual, this release contains a bunch of
 important fixes and a slew of new and improved features. Please upgrade ASAP.