Repository: conda/conda

Issue:
conda-env update error in 4.3.20
```
conda env update
An unexpected error has occurred.
Please consider posting the following information to the
conda GitHub issue tracker at:
    https://github.com/conda/conda/issues
Current conda install:
               platform : linux-64
          conda version : 4.3.20
       conda is private : False
      conda-env version : 4.3.20
    conda-build version : not installed
         python version : 3.5.2.final.0
       requests version : 2.14.2
       root environment : /home/travis/miniconda  (writable)
    default environment : /home/travis/miniconda
       envs directories : /home/travis/miniconda/envs
                          /home/travis/.conda/envs
          package cache : /home/travis/miniconda/pkgs
                          /home/travis/.conda/pkgs
           channel URLs : https://conda.anaconda.org/conda-canary/linux-64
                          https://conda.anaconda.org/conda-canary/noarch
                          https://repo.continuum.io/pkgs/free/linux-64
                          https://repo.continuum.io/pkgs/free/noarch
                          https://repo.continuum.io/pkgs/r/linux-64
                          https://repo.continuum.io/pkgs/r/noarch
                          https://repo.continuum.io/pkgs/pro/linux-64
                          https://repo.continuum.io/pkgs/pro/noarch
            config file : /home/travis/.condarc
             netrc file : None
           offline mode : False
             user-agent : conda/4.3.20 requests/2.14.2 CPython/3.5.2 Linux/4.4.0-51-generic debian/jessie/sid glibc/2.19    
                UID:GID : 1000:1000
`$ /home/travis/miniconda/bin/conda-env update`
    Traceback (most recent call last):
      File "/home/travis/miniconda/lib/python3.5/site-packages/conda/exceptions.py", line 632, in conda_exception_handler
        return_value = func(*args, **kwargs)
      File "/home/travis/miniconda/lib/python3.5/site-packages/conda_env/cli/main_update.py", line 82, in execute
        if not (args.name or args.prefix):
    AttributeError: 'Namespace' object has no attribute 'prefix'
```


Discussion:

Resolving patch:
diff --git a/conda_env/cli/main_update.py b/conda_env/cli/main_update.py
--- a/conda_env/cli/main_update.py
+++ b/conda_env/cli/main_update.py
@@ -1,18 +1,16 @@
 from argparse import RawDescriptionHelpFormatter
 import os
-import textwrap
 import sys
+import textwrap
 
-from conda import config
-from conda.cli import common
-from conda.cli import install as cli_install
+from conda.cli import common, install as cli_install
 from conda.misc import touch_nonadmin
-from ..installers.base import get_installer, InvalidInstaller
-from .. import specs as install_specs
-from .. import exceptions
 # for conda env
 from conda_env.cli.common import get_prefix
+from .. import exceptions, specs as install_specs
 from ..exceptions import CondaEnvException
+from ..installers.base import InvalidInstaller, get_installer
+
 description = """
 Update the current environment based on environment file
 """
@@ -35,12 +33,7 @@ def configure_parser(sub_parsers):
         help=description,
         epilog=example,
     )
-    p.add_argument(
-        '-n', '--name',
-        action='store',
-        help='name of environment (in %s)' % os.pathsep.join(config.envs_dirs),
-        default=None,
-    )
+    common.add_parser_prefix(p)
     p.add_argument(
         '-f', '--file',
         action='store',


Test patch: