Add an explicit build-dependency on python3-yaml since livecd-rootfs uses it, rather than relying on this dependency being pulled in indirectly via ubuntu-image.

debian/changelog

@@ -1,3 +1,11 @@
+livecd-rootfs (2.588) UNRELEASED; urgency=medium
+
+  * Add an explicit build-dependency on python3-yaml since livecd-rootfs
+    uses it, rather than relying on this dependency being pulled in
+    indirectly via ubuntu-image.
+
+ -- Steve Langasek <steve.langasek@ubuntu.com>  Thu, 30 May 2019 14:22:25 -0700
+
 livecd-rootfs (2.587) eoan; urgency=medium
 
   * Strip translation files out of the minimal images, another thing that

debian/control

@@ -31,6 +31,7 @@ Depends: ${misc:Depends},
          python3,
          python3-apt,
          python3-software-properties,
+         python3-yaml,
          qemu-utils,
          rsync,
          snapd,