fix bootswatch_theme command

[areski]

Command bootswatch_theme is now fixed for bootstrap3 and boostrap2

[Kwpolska]

You have commit rights, why not do it yourself on this repo?

Also, bootstrap 2 is the default theme right now.

[areski]

I can press the merge button, I know... but opening it, it's a nice way to discuss it before merging.
I'm being cautious for the moment, but things that are straightforward I will commit directly.

Yes bootstrap2 is default for nikola, but bootstrap3 is default for bootswatch

[ralsina]

I don't quite see the point of this change. It doesn't seem to hurt anything either, tho, so... ok! :-)

[areski]

@ralsina
The important part is:

-            'default': 'site',
-            'help': 'Parent theme name (default: site)',
+            'default': 'bootstrap3',
+            'help': 'Parent theme name (default: bootstrap3)',

'site' doesnt' exist anymore

[ralsina]

@areski Ah, good catch there!