Update mender-convert to use final Mender v2.0 release

Changelog: Title

Signed-off-by: Lluis Campos <lluis.campos@northern.tech>
(cherry picked from commit 1a6c4126be)

Dockerfile

@@ -1,6 +1,6 @@
 FROM ubuntu:18.04
 
-ARG MENDER_ARTIFACT_VERSION=3.0.0b1
+ARG MENDER_ARTIFACT_VERSION=3.0.0
 ARG GOLANG_VERSION=1.11.2
 
 RUN apt-get update && apt-get install -y \

device-image-shell/Dockerfile

@@ -1,6 +1,6 @@
 FROM ubuntu:18.04
 
-ARG MENDER_ARTIFACT_VERSION=3.0.0b1
+ARG MENDER_ARTIFACT_VERSION=3.0.0
 
 RUN apt-get update && apt-get install -y \
     wget \

docker-build

@@ -4,6 +4,6 @@ set -e
 
 IMAGE_NAME=mender-convert
 
-MENDER_CLIENT_VERSION="2.0.0b1"
+MENDER_CLIENT_VERSION="2.0.0"
 
 docker build . -t ${IMAGE_NAME} --build-arg mender_client_version=${MENDER_CLIENT_VERSION}