fixed bug, not being able to write code on the first line

[KianBahasadri]

Hello, first of all this is my first pull request. (Sorry if I dont really know what I'm doing)
Second of all, pybash currently gets a syntax error anytime it parses a file that has code on the first line, this is because of this line in import_hook.py:

180         if self.source_init is not None:
181             source = self.source_init() + source

Its basically doing "import subprocess" + source, which concatenates the import line and the first line of the code.
I changed it to "import subprocess\n" so that the import stays on its own line.

p.s. your project is really cool, thanks for making it :)

[jaykv]

Thanks for fixing this! I'll get this out in a new version.

Glad you like the project :)