devtool: use kcov enabled image v18

Signed-off-by: Diana Popa <[email protected]>

Author: dianpopa

tools/devtool

@@ -73,7 +73,7 @@
 # Development container image (name:tag)
 # This should be updated whenever we upgrade the development container.
 # (Yet another step on our way to reproducible builds.)
-DEVCTR_IMAGE="fcuvm/dev:v16"
+DEVCTR_IMAGE="fcuvm/dev:v18"
 
 # Naming things is hard
 MY_NAME="Firecracker $(basename "$0")"