Update CHANGELOG - v0.15.0

Signed-off-by: Joffrey F <joffrey@docker.com>

CHANGELOG.md

 # Changelog
 
+# 0.15.0 (2018-06-12)
+
+## General
+
+- `docker-machine` can now be installed using `go install`.
+- Now built with go 1.10
+- Added keep-alive to SSH connections (#4450)
+
+## Drivers
+
+### amazonec2
+
+- Updated default AMIs to mitigate Meltdown and Spectre
+- Added `--amazonec2-security-group-readonly` flag to prevent mutating security groups
+
+### exoscale
+
+- Updated driver to v0.9.23
+
+### hyperv
+
+- Fixed Hyper-V pre-create issues (#4426)
+- Added the ability to disable Hyper-V dynamic memory management during VM creation (`--hyperv-disable-dynamic-memory`)
+
+### vmwarefusion
+
+- Improved shell checks (#4491)
+
+
 # 0.14.0 (2018-03-06)
 
 ## General