Kickoff 2018.05 cycle

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

Makefile

@@ -87,7 +87,7 @@ all:
 .PHONY: all
 
 # Set and export the version string
-export BR2_VERSION := 2018.02
+export BR2_VERSION := 2018.05-git
 # Actual time the release is cut (for reproducible builds)
 BR2_VERSION_EPOCH = 1520198000