Compatibility with MkDocs 1.2: livereload isn't guaranteed now

MkDocs doesn't depend on 'livereload' library, and neither should we, but we import it for the type annotation, which is now also wrong

pyproject.toml

@@ -19,7 +19,7 @@ python = "^3.6"
 Jinja2 = ">=2.11.1, <4.0"
 Markdown = "^3.3"
 MarkupSafe = ">=1.1, <3.0"
-mkdocs = "^1.1"
+mkdocs = "^1.1.1"
 mkdocs-autorefs = ">=0.1, <0.3"
 pymdown-extensions = ">=6.3, <9.0"
 pytkdocs = ">=0.2.0, <0.12.0"

src/mkdocstrings/plugin.py

@@ -20,7 +20,6 @@
 import urllib.request
 from typing import Any, BinaryIO, Callable, Iterable, List, Mapping, Optional, Tuple
 
-from livereload import Server
 from mkdocs.config import Config
 from mkdocs.config.config_options import Type as MkType
 from mkdocs.plugins import BasePlugin
@@ -111,7 +110,7 @@ def handlers(self) -> Handlers:
             raise RuntimeError("The plugin hasn't been initialized with a config yet")
         return self._handlers
 
-    def on_serve(self, server: Server, builder: Callable = None, **kwargs) -> Server:  # noqa: W0613 (unused arguments)
+    def on_serve(self, server, builder: Callable, **kwargs):  # noqa: W0613 (unused arguments)
         """Watch directories.
 
         Hook for the [`on_serve` event](https://www.mkdocs.org/user-guide/plugins/#on_serve).
@@ -127,10 +126,6 @@ def on_serve(self, server: Server, builder: Callable = None, **kwargs) -> Server
         Returns:
             The server instance.
         """
-        if builder is None:
-            # The builder parameter was added in mkdocs v1.1.1.
-            # See issue https://github.com/mkdocs/mkdocs/issues/1952.
-            builder = list(server.watcher._tasks.values())[0]["func"]  # noqa: W0212 (protected member)
         for element in self.config["watch"]:
             log.debug(f"Adding directory '{element}' to watcher")
             server.watch(element, builder)