text: Title: [Bug]  SyntaxError: invalid syntax after installing the library
  Body: I'm getting SyntaxError: invalid syntax after installing the library
  
  Traceback (most recent call last):
    File "script.py", line 1, in <module>
      import twelvedata
    File "/Users/work/Library/Python/2.7/lib/python/site-packages/twelvedata/__init__.py", line 3, in <module>
      from .client import TDClient
    File "/Users/work/Library/Python/2.7/lib/python/site-packages/twelvedata/client.py", line 2, in <module>
      from .endpoints import (
    File "/Users/work/Library/Python/2.7/lib/python/site-packages/twelvedata/endpoints.py", line 113
      def get_symbol(symbol) -> (str, bool):
                             ^
  SyntaxError: invalid syntax
  
  
  **To Reproduce**
  Steps to reproduce the behavior:
  1- pip install twelvedata
  2- in script.py:  from twelvedata import TDClient
  3- run python script.py
  
  
  
  