Update rules_docker version in WORKSPACE

[wood-jp]

Look like the current version is using rules_docker v0.10.1

But since then rules_docker has removed python2 in favour of python3 (and is now at version v0.25.0)

The issue being that it's not possible to use this on a system that does not have python2 installed, like github for example. Attempting to do so will fail with a message like this one:

++ python -c 'import sys,json; print json.dumps(sys.stdin.read().strip().split())'
  File "<string>", line 1
    import sys,json; print json.dumps(sys.stdin.read().strip().split())
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
SyntaxError: Missing parentheses in call to 'print'. Did you mean print(...)?
+ fmt_cmd=