python2 called explicitly

[FelixTheStudent]

Hi bulik,

I tried running ldsc -h in a Anaconda3 environment (much like issue #178) and got the following error:

./ldsc.py -h

  File "./ldsc.py", line 84
    print msg
            ^
SyntaxError: Missing parentheses in call to 'print'. Did you mean print(msg)?

Turns out the problem is that ldsc.py calls python with '#!/usr/bin/env python', which will call either python2 or python3 depending on how a user has set up his python (Anaconda) installation.

This pull request I am sending you today changes the one line above to '#!/usr/bin/env python2'. This solves this issue, i.e. './ldsc.py -h' prints out the list of all command-line options, as intended. I have not tried running ldsc.py on any data yet, I hope you could test this.

Cheers,

Felix