[19.03] Dockerfile: move CRIU_VERSION lower

Match the position with where it's on master after the
Dockerfile buildkit refactor.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

Dockerfile

@@ -37,8 +37,6 @@ ENV GO111MODULE=off
 
 FROM base AS criu
 ARG DEBIAN_FRONTEND
-# Install CRIU for checkpoint/restore support
-ENV CRIU_VERSION 3.12
 # Install dependency packages specific to criu
 RUN apt-get update && apt-get install -y --no-install-recommends \
 	libnet-dev \
@@ -50,6 +48,9 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
 	protobuf-c-compiler \
 	python-protobuf \
 	&& rm -rf /var/lib/apt/lists/*
+
+# Install CRIU for checkpoint/restore support
+ENV CRIU_VERSION 3.12
 RUN mkdir -p /usr/src/criu \
 	&& curl -sSL https://github.com/checkpoint-restore/criu/archive/v${CRIU_VERSION}.tar.gz | tar -C /usr/src/criu/ -xz --strip-components=1 \
 	&& cd /usr/src/criu \