Default branch rename

Helps with whatwg/meta#174.

PULL_REQUEST_TEMPLATE.md.template

@@ -7,7 +7,7 @@ Thank you for contributing to the @@h1@@ Standard! Please describe the change yo
    * …
 - [ ] [Tests](https://github.com/web-platform-tests/wpt) are written and can be reviewed and commented upon at:
    * …
-- [ ] [Implementation bugs](https://github.com/whatwg/meta/blob/master/MAINTAINERS.md#handling-pull-requests) are filed:
+- [ ] [Implementation bugs](https://github.com/whatwg/meta/blob/main/MAINTAINERS.md#handling-pull-requests) are filed:
    * Chrome: …
    * Firefox: …
    * Safari: …

factory.py

@@ -70,7 +70,7 @@ def update(templates, variables):
 
     files = fill_templates(templates, variables)
 
-    subprocess.run(["git", "checkout", "master"], capture_output=True)
+    subprocess.run(["git", "checkout", "main"], capture_output=True)
     subprocess.run(["git", "pull"], capture_output=True)
     for file in files:
         if variables["only_these_templates"] and file not in variables["only_these_templates"]:
@@ -94,7 +94,7 @@ def update(templates, variables):
 
 def main():
     templates = gather_templates()
-    db = json.loads(requests.get("https://github.com/whatwg/sg/raw/master/db.json").text)
+    db = json.loads(requests.get("https://github.com/whatwg/sg/raw/main/db.json").text)
     local_db = json.loads(read_file("factory.json"))
     for workstream in db["workstreams"]:
         for standard in workstream["standards"]: