bump iso on head

Makefile

@@ -23,7 +23,7 @@ KUBERNETES_VERSION ?= $(shell egrep "DefaultKubernetesVersion =" pkg/minikube/co
 KIC_VERSION ?= $(shell egrep "Version =" pkg/drivers/kic/types.go | cut -d \" -f2)
 
 # Default to .0 for higher cache hit rates, as build increments typically don't require new ISO versions
-ISO_VERSION ?= v1.14.0
+ISO_VERSION ?= v1.15.0-snapshot1
 # Dashes are valid in semver, but not Linux packaging. Use ~ to delimit alpha/beta
 DEB_VERSION ?= $(subst -,~,$(RAW_VERSION))
 RPM_VERSION ?= $(DEB_VERSION)