bump version to v1.7.99

This starts development on master for Zephyr 1.8

Change-Id: I81484f09cd4ed90c276f2901be90132af90c2208
Signed-off-by: Anas Nashif <anas.nashif@intel.com>
diff --git a/Makefile b/Makefile
index db44eae..d09d2c2 100644
--- a/Makefile
+++ b/Makefile
@@ -1,5 +1,5 @@
 VERSION_MAJOR 	   = 1
-VERSION_MINOR 	   = 6
+VERSION_MINOR 	   = 7
 PATCHLEVEL 	   = 99
 VERSION_RESERVED   = 0
 EXTRAVERSION       =