Revert "Upgrade kaniko version to 1.7.0 (#37)"

This reverts commit 0a4b18dbcb.

Kaniko 1.7.0 version is unable to push latest tag on gcr:
https://github.com/GoogleContainerTools/kaniko/issues/1786#issuecomment-951369997

docker/docker/Dockerfile.linux.amd64

@@ -1,4 +1,4 @@
-FROM gcr.io/kaniko-project/executor:v1.7.0
+FROM gcr.io/kaniko-project/executor:v1.6.0
 
 ADD release/linux/amd64/kaniko-docker /kaniko/
 ENTRYPOINT ["/kaniko/kaniko-docker"]

docker/docker/Dockerfile.linux.arm64

@@ -1,4 +1,4 @@
-FROM gcr.io/kaniko-project/executor:v1.7.0
+FROM gcr.io/kaniko-project/executor:arm64-v1.6.0
 
 ENV HOME /root
 ENV USER root

docker/ecr/Dockerfile.linux.amd64

@@ -1,4 +1,4 @@
-FROM gcr.io/kaniko-project/executor:v1.7.0
+FROM gcr.io/kaniko-project/executor:v1.6.0
 
 ADD release/linux/amd64/kaniko-ecr /kaniko/
 ENTRYPOINT ["/kaniko/kaniko-ecr"]

docker/ecr/Dockerfile.linux.arm64

@@ -1,4 +1,4 @@
-FROM gcr.io/kaniko-project/executor:v1.7.0
+FROM gcr.io/kaniko-project/executor:arm64-v1.6.0
 
 ENV HOME /root
 ENV USER root

docker/gcr/Dockerfile.linux.amd64

@@ -1,4 +1,4 @@
-FROM gcr.io/kaniko-project/executor:v1.7.0
+FROM gcr.io/kaniko-project/executor:v1.6.0
 
 ADD release/linux/amd64/kaniko-gcr /kaniko/
 ENTRYPOINT ["/kaniko/kaniko-gcr"]

docker/gcr/Dockerfile.linux.arm64

@@ -1,4 +1,4 @@
-FROM gcr.io/kaniko-project/executor:v1.7.0
+FROM gcr.io/kaniko-project/executor:arm64-v1.6.0
 
 ENV HOME /root
 ENV USER root