Fix docstrings that intend '\' literally

This intended '\' literally, but it was actually '' because the \'
became just ' (backslash-apostrophe becomes just aspostrophe).

git/objects/base.py

@@ -212,7 +212,7 @@ def name(self) -> str:
 
     @property
     def abspath(self) -> PathLike:
-        """
+        R"""
         :return:
             Absolute path to this index object in the file system ( as opposed to the
             .path field which is a path relative to the git repository ).

git/util.py

@@ -239,7 +239,7 @@ def stream_copy(source: BinaryIO, destination: BinaryIO, chunk_size: int = 512 *
 
 
 def join_path(a: PathLike, *p: PathLike) -> PathLike:
-    """Join path tokens together similar to osp.join, but always use
+    R"""Join path tokens together similar to osp.join, but always use
     '/' instead of possibly '\' on windows."""
     path = str(a)
     for b in p:
@@ -277,7 +277,7 @@ def to_native_path_linux(path: PathLike) -> str:
 
 
 def join_path_native(a: PathLike, *p: PathLike) -> PathLike:
-    """
+    R"""
     As join path, but makes sure an OS native path is returned. This is only
         needed to play it safe on my dear windows and to assure nice paths that only
         use '\'"""