Fixes #55 Change tag separator to match with Shaarli

[amadeous]

Changing ", " to " " will return a list of tags separated by " " instead of ", " when fetching tags to post link to Shaarli.

This makes it consistent with the UI instructing to use spaces as tag separator (here).

A future improvement could be to allow the user to define a specific tag separator for the current Shaarli instance they are posting to.

[amadeous]

This PR fixes #55 (should be linked to issue but isn't for some reason).

I could try to add the future improvement mentioned above, if @dimtion is willing to integrated it to the app.

[amadeous]

@dimtion Could you please moderate this PR? It should not take long (the modification is literally one char).