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Chrome driver permission problem

tldr; /usr/local/bin/chromedriver is not executable (needs chmod +x)

I am not able to get selenium/splinter to work due to permission issues.
I set the paths as per https://morph.io/documentation/scraping_javascript_sites:

chrome_options = ChromeOptions()
chrome_options.binary_location = '/usr/bin/google-chrome'
chrome_options.add_argument('--headless')
chrome_options.add_argument('--disable-gpu')

with Browser('chrome', executable_path='/usr/local/bin/chromedriver', headless=True, options=chrome_options) as browser:
    browser.visit(URL)

But getting the following stack trace (see https://morph.io/dcalde/cityperthscraper)

Traceback (most recent call last):
  File "scraper.py", line 47, in <module>
    with Browser('chrome', executable_path='/usr/local/bin/chromedriver', headless=True, options=chrome_options) as browser:
  File "/app/.heroku/python/lib/python3.6/site-packages/splinter/browser.py", line 92, in Browser
    return get_driver(driver, *args, **kwargs)
  File "/app/.heroku/python/lib/python3.6/site-packages/splinter/browser.py", line 70, in get_driver
    raise err
  File "/app/.heroku/python/lib/python3.6/site-packages/splinter/browser.py", line 66, in get_driver
    return driver(*args, **kwargs)
  File "/app/.heroku/python/lib/python3.6/site-packages/splinter/driver/webdriver/chrome.py", line 43, in __init__
    self.driver = Chrome(options=options, **kwargs)
  File "/app/.heroku/python/lib/python3.6/site-packages/selenium/webdriver/chrome/webdriver.py", line 73, in __init__
    self.service.start()
  File "/app/.heroku/python/lib/python3.6/site-packages/selenium/webdriver/common/service.py", line 88, in start
    os.path.basename(self.path), self.start_error_message)
selenium.common.exceptions.WebDriverException: Message: 'chromedriver' executable may have wrong permissions. Please see https://sites.google.com/a/chromium.org/chromedriver/home

I checked the file permissions, and while chrome itself is executable, chrome driver isn’t (at least not the user):
/usr/local/bin/chromedriver: -rwx------
/usr/bin/google-chrome: -rwxr-xr-x