[FAB-11043] Remove "-stable" suffix in upgrade docs

In docker hub, there is no "-stable" tag for fabric images.
However, "-stable" tag is written in upgrade docs and
upgrades steps fail. This CR removes "-stable" tag.

FAB-11043 #done

Change-Id: I85c9b7c5b39c09c1ac331cb226fe5dae67e26707
Signed-off-by: Nao Nishijima <nao.nishijima@hal.hitachi.com>

docs/source/upgrading_your_network_tutorial.rst

@@ -214,7 +214,7 @@ Let’s begin the upgrade process by **bringing down the orderer**:
  # Note, replace '1.3.x' with a specific version, for example '1.3.0'.
  # Set IMAGE_TAG to 'latest' if you prefer to default to the images tagged 'latest' on your system.
 
- export IMAGE_TAG=$(go env GOARCH)-1.3.x-stable
+ export IMAGE_TAG=$(go env GOARCH)-1.3.x
 
 We have created a variable for a directory to put file backups into, and
 exported the ``IMAGE_TAG`` we'd like to move to.
@@ -343,7 +343,7 @@ If you specifically want the v1.3 version of the CLI, issue:
 
 .. code:: bash
 
- IMAGE_TAG=$(go env GOARCH)-1.3.x-stable docker-compose -f docker-compose-cli.yaml up -d --no-deps cli
+ IMAGE_TAG=$(go env GOARCH)-1.3.x docker-compose -f docker-compose-cli.yaml up -d --no-deps cli
 
 Once you have the version of the CLI you want, get into the CLI container: