Update release notes with 1.4 release
# RELEASE NOTES
-30 November 2017 - Apache Mynewt v1.3.0
+04 June 2018 - Apache Mynewt v1.4.0
For full release notes, please visit the
[Apache Mynewt Wiki](https://cwiki.apache.org/confluence/display/MYNEWT/Release+Notes).
