Fixed kernel headers in offline repo

contrib/rootfs/offline_repo.json

@@ -96,6 +96,7 @@
             "pkgdescription": "Vanilla Linux Kernel Headers",
             "tagged": false,
             "urls": [
+              "http://kernel.ubuntu.com/~kernel-ppa/mainline/v4.14-rc3/linux-headers-4.14.0-041400rc3_4.14.0-041400rc3.201710011930_all.deb",
               "http://kernel.ubuntu.com/~kernel-ppa/mainline/v4.14-rc3/linux-headers-4.14.0-041400rc3-generic_4.14.0-041400rc3.201710011930_amd64.deb",
               "http://kernel.ubuntu.com/~kernel-ppa/mainline/v4.14-rc3/linux-headers-4.14.0-041400rc3-generic_4.14.0-041400rc3.201710011930_i386.deb"
             ]