解决 树莓派使用gstreamer 报错ImportError: cannot import name xxx introspection typelib not found

Gstreamer是一个视频流框架，安装后初次使用 ，使用官方doc中的hello world 例程 会报错，如下：

importError: cannot import name GstRtspServer, introspection typelib not found

```python
#!/usr/bin/env python3
import sys

import gi

gi.require_version('GLib', '2.0')
gi.require_version('GObject', '2.0')
gi.require_version('Gst', '1.0')

from gi.repository import Gst, GObject, GLib

pipeline = None
bus = None
message = None

# initialize GStreamer
Gst.init(sys.argv[1:])

# build the pipeline
pipeline = Gst.parse_launch(
    "playbin uri=https://www.freedesktop.org/software/gstreamer-sdk/data/media/sintel_trailer-480p.webm"
)

# start playing
pipeline.set_state(Gst.State.PLAYING)

# wait until EOS or error
bus = pipeline.get_bus()
msg = bus.timed_pop_filtered(
    Gst.CLOCK_TIME_NONE,
    Gst.MessageType.ERROR | Gst.MessageType.EOS
)

# free resources
pipeline.set_state(Gst.State.NULL)

sudo apt-get install gir1.2-gst-rtsp-server-1.0