title: Conda cannot install pydot-ng with python3 (Unsatisfiable error)
body: <p>I have Anaconda 4.3.23 on Ubuntu 16.04 LTS. When I try to install pydot-ng package using</p>
  
  <pre><code>conda install pydot-ng
  </code></pre>
  
  <p>I get the following error:</p>
  
  <pre><code>UnsatisfiableError: The following specifications were found to be in conflict:
  - pydot-ng -&gt; python 2.7* -&gt; openssl 1.0.1*
  - python 3.6*
  Use "conda info &lt;package&gt;" to see the dependencies for each package.
  </code></pre>
  
  <p>Upon running  <code>conda info pydot-ng</code> i see</p>
  
  <pre><code>pydot-ng 1.0.0.15 py27_0
  ------------------------
  file name   : pydot-ng-1.0.0.15-py27_0.tar.bz2
  name        : pydot-ng
  version     : 1.0.0.15
  build string: py27_0
  build number: 0
  channel     : defaults
  size        : 45 KB
  arch        : x86_64
  date        : 2015-09-09
  license     : MIT
  md5         : 8b81a344723e64ec3545b5f030caca47
  noarch      : None
  platform    : linux
  url         : https://repo.continuum.io/pkgs/free/linux-64/pydot-ng-
  1.0.0.15-py27_0.tar.bz2
  dependencies:
     pyparsing
     python 2.7*
  
  pydot-ng 1.0.0.15 py34_0
  ------------------------
  file name   : pydot-ng-1.0.0.15-py34_0.tar.bz2
  name        : pydot-ng
  version     : 1.0.0.15
  build string: py34_0
  build number: 0
  channel     : defaults
  size        : 46 KB
  arch        : x86_64
  date        : 2015-09-09
  license     : MIT
  md5         : 13e3a10b45edfb38d91a51d6b3ccabc7
  noarch      : None
  platform    : linux
  url         : https://repo.continuum.io/pkgs/free/linux-64/pydot-ng-
  1.0.0.15-py34_0.tar.bz2
  dependencies:
     pyparsing
     python 3.4*
  </code></pre>
  
  <p>What is the problem? Shouldn't conda be able to install the <code>pydot-ng 1.0.0.15 py34_0</code> version which would be compatible with python 3.6 (I presume)?</p>