cli: explicitly set show_envvar=False for --provider

It is false by default, but specify anyways for clarity
(and defensively in case of upstream changes in defaults).

Signed-off-by: Chris Patterson <chris.patterson@canonical.com>

snapcraft/cli/_options.py

@@ -83,6 +83,7 @@ def prompt_for_value(self, ctx):
     dict(
         param_decls="--provider",
         envvar="SNAPCRAFT_BUILD_ENVIRONMENT",
+        show_envvar=False,
         help="Build provider to use.",
         metavar="[{}]".format("|".join(_SUPPORTED_PROVIDERS)),
         type=click.Choice(_SUPPORTED_PROVIDERS + _HIDDEN_PROVIDERS),