Really quick way to make sure your Sublime Text is using Python 3 to run your code. I've edited this a bit. If you still have problems, visit the original repo and check the comments.

How to link Sublime Text Build system to Python 3

Check out my video tutorial here: 
https://www.youtube.com/watch?v=IprbE2C_rsE

1. Make sure you save your file with a .py extension before trying to build/run it. 
If you try to build before saving, it won't work.

2. Go to Sublime Text to: Tools -> Build System -> New Build System 
and delete whatever is there. Copy and paste the following onto the empty file:

{
    "cmd": ["python3", "-i", "-u", "$file"],
    "file_regex": "^[ ]File \"(...?)\", line ([0-9]*)",
    "selector": "source.python"
}

Then save it (save it in the default directory that shows up when you press Save As) 
with a meaningful name like: python3.sublime-build


3. Go to Tools -> Build system -> and check python3 

test it with:

import sys
print(sys.version)

Press: 
    Ctrl b (Windows) 
    Cmd b (Mac)