remove -v from conda env update

there is so much verbose output that it seems to make it even harder to see what's happening,
except in very particular

while it's useful for debugging purposes when things like post-link fail,
I don't think we should do it by default.

added a `conda list` at the end to see what's been installed

repo2docker/buildpacks/conda/__init__.py

@@ -117,8 +117,9 @@ class CondaBuildPack(BaseImage):
             assembly_scripts.append((
                 '${NB_USER}',
                 r"""
-                conda env update -v -n {} -f "{}" && \
-                conda clean -tipsy
+                conda env update -n {0} -f "{1}" && \
+                conda clean -tipsy && \
+                conda list -n {0}
                 """.format(env_name, environment_yml)
             ))
         return super().get_assemble_scripts() + assembly_scripts