Display an error instead of aborting

[wilfriedb]

See issue #29.
If myget.org can't be reached, the script will show the next message in the Sublime Text console:

URL error [Errno -2] Name or service not known contacting API

instead of

Traceback (most recent call last):
  File "/opt/sublime_text/sublime_plugin.py", line 97, in reload_plugin
    obj = t()
  File "/home/username/.config/sublime-text-3/Packages/Kulture/Completions.py", line 27, in __init__
    for package in response:
TypeError: 'bool' object is not iterable

[sayedihashimi]

Thanks for the PR, can you tell me what platforms you tested this on?

[wilfriedb]

Yes of course. I've tested it on Windows 7 and Linux Mint 7.1, both with Sublime Text version 3, both with and without network connection.

The reason I made this pull request is that at my company the Completions.py aborted and I didn't know why. I thought it was the setup of my PC but later I found out that Sublime can't pass the company's proxy. I thought an error message would be more helpful than an abort and actually the script does check for errors but then ignores the result. So I made this small modification that displays the error message to the user.

[sayedihashimi]

Thanks for the contribution!