Make bash as default shell on Linux (UsergeTeam#537)

* Make bash as default shell on unix

* Forgot the walrus eyes ...

userge/plugins/builtin/executor/__main__.py

@@ -20,6 +20,7 @@
 from contextlib import contextmanager
 from enum import Enum
 from getpass import getuser
+from shutil import which
 from typing import Awaitable, Any, Callable, Dict, Optional, Tuple, Iterable
 
 import aiofiles
@@ -464,6 +465,8 @@ async def execute(cls, cmd: str) -> 'Term':
             stderr=asyncio.subprocess.PIPE)
         if setsid:
             kwargs['preexec_fn'] = setsid
+        if sh := which(os.environ.get("USERGE_SHELL", "bash")):
+            kwargs['executable'] = sh
         process = await asyncio.create_subprocess_shell(cmd, **kwargs)
         t_obj = cls(process)
         t_obj._start()