Repository: manuzhang/mkdocs-htmlproofer-plugin (language: python)

Issue:
request headers
In my docs I link to an external web site that always give a 404 with the plugin (I'm guessing it's a bot mitigation).  I narrowed down what it seems to need with this example:

```
import requests

url = 'https://www.imhpromotion.ca'
print(requests.get(url=url))
print(requests.get(url=url,headers={'Accept-Language': 'en-US,en;q=0.9'}))
```

It would be nice to be able to customise the header.  

I should probably use the `raise_error_excludes` setting, but would like to know if that site goes down.



Discussion / hints:
Thanks, I think I will set the `Accept-Language` to `*` for any language.

Fix patch:
diff --git a/htmlproofer/plugin.py b/htmlproofer/plugin.py
index 48c816e..731f611 100644
--- a/htmlproofer/plugin.py
+++ b/htmlproofer/plugin.py
@@ -18,7 +18,7 @@
 
 URL_TIMEOUT = 10.0
 _URL_BOT_ID = f'Bot {uuid.uuid4()}'
-URL_HEADERS = {'User-Agent': _URL_BOT_ID}
+URL_HEADERS = {'User-Agent': _URL_BOT_ID, 'Accept-Language': '*'}
 
 EXTERNAL_URL_PATTERN = re.compile(r'https?://')
 MARKDOWN_ANCHOR_PATTERN = re.compile(r'(.+)#(.+)')


Test patch:
diff --git a/tests/integration/docs/page4.md b/tests/integration/docs/page4.md
index 31957da..77cd1e7 100644
--- a/tests/integration/docs/page4.md
+++ b/tests/integration/docs/page4.md
@@ -1,4 +1,4 @@
 ## Section One
 
-
-[This site](https://marketplace.visualstudio.com/items?itemName=ms-python.python) doesn't work with `HEAD` requests.
\ No newline at end of file
+* [This site](https://marketplace.visualstudio.com/items?itemName=ms-python.python) doesn't work with `HEAD` requests.
+* [This site](https://www.imhpromotion.ca) needs `headers={'Accept-Language': '*'}`