Fix cyrillic path

Hello!
I've found that latest version of a script is failed to execute when --path contains cyrillic symbols (python2.7 coursera-dl -u username -p 'password' --path "/home/leonid/Downloads/темп1" digitalsounddesign-002) on Ubuntu 14.04 LTS. I installed all requirements. "UnicodeDecodeError: 'ascii' codec can't decode byte 0xd1 in position 23: ordinal not in range(128)" occur in os.path.join function. So I added explicit path decoding to text type with sys.input.encoding. Hope this will be useful.