disables docker upgrade, need more investigation

- disables buildkit

.travis.yml

@@ -1,24 +1,19 @@
 language: minimal
-sudo: required
 services:
-- docker
+  - docker
-before_install:
-- curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add -
-- sudo add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable"
-- sudo apt-get -q update
-- sudo apt-get -y -o Dpkg::Options::="--force-confnew" install docker-ce
 addons:
   apt:
     update: true
     packages:
-    - curl
+      - curl
-    - openssl
+      - openssl
-    - ca-certificates
+      - ca-certificates
-    - make
+      - make
-    - qemu-user-static
+      - qemu-user-static
 env:
   global:
     - PARALLELMFLAGS="-j4"
+    - DOCKER_BUILDKIT=0
   matrix:
     - DISTRIB_ID=ubuntu VARIANT=debug        MARCH=x86_64   CHECK_TARGET=memcheck
     - DISTRIB_ID=ubuntu VARIANT=coverage     MARCH=x86_64   CHECK_TARGET=check