Prompt is in double parentheses

[Christian Ullrich]

mkvirtualenv.bat sets the prompt prefix for the virtualenv by enclosing its name in parentheses and appending a space. Since pypa/virtualenv#2224 virtualenv itself does the same, so now the prompt looks like this after activating a virtualenv named "dj":

((dj ) ) C:\...>

[Bjorn]

Thanks for the report. Fixed in latest version.