npm update without of --unsafe-perm broke the ffmpeg plug-in
**Describe the bug**
I don't think this is `homebridge-nest-cam` bug per say, but it would be nice to have some sort of "howto" to fix this problem.

After I upgraded all packages using the following command:

```
sudo npm -g update
```

I noticed a message which said that `ffmpeg` update failed. I realized that I was missing the `--unsafe-perm` parameter and updated the `ffmpeg` package explicitly (with that parameter). The `ffmpeg` got updated (to version 0.0.9), but ever since I'm getting this error when I'm trying to open the live stream:

```
[9/9/2020, 2:26:20 PM] [Nest-cam] FFMPEG is not installed. Please install it before using this plugin.
```

There are no extra messages even in debug mode.

I guess it is failing to locate the binary in the path, but I couldn't figure out why:

```
/usr/local/lib/node_modules/ffmpeg-for-homebridge/ffmpeg 
ffmpeg version 4.3.1 Copyright (c) 2000-2020 the FFmpeg developers
  built with gcc 6.3.0 (Debian 6.3.0-18+deb9u1) 20170516
  configuration: --pkgconfigdir=/build/workspace/lib/pkgconfig --prefix=/build/workspace --pkg-config-flags=--static --extra-cflags=-I/build/workspace/include --extra-ldflags=-L/build/workspace/lib --extra-libs='-lpthread -lm' --enable-static --disable-debug --disable-shared --disable-ffplay --disable-doc --enable-openssl --enable-gpl --enable-version3 --enable-nonfree --enable-pthreads --enable-libvpx --enable-libmp3lame --enable-libopus --enable-libtheora --enable-libvorbis --enable-libx264 --enable-runtime-cpudetect --enable-libfdk-aac --enable-avfilter --enable-libopencore_amrwb --enable-libopencore_amrnb --enable-filters --enable-decoder=h264 --enable-network --enable-protocol=tcp --enable-libspeex --enable-demuxer=rtsp --enable-indev=alsa --enable-outdev=alsa
  libavutil      56. 51.100 / 56. 51.100
  libavcodec     58. 91.100 / 58. 91.100
  libavformat    58. 45.100 / 58. 45.100
  libavdevice    58. 10.100 / 58. 10.100
  libavfilter     7. 85.100 /  7. 85.100
  libswscale      5.  7.100 /  5.  7.100
  libswresample   3.  7.100 /  3.  7.100
  libpostproc    55.  7.100 / 55.  7.100
Hyper fast Audio and Video encoder
usage: ffmpeg [options] [[infile options] -i infile]... {[outfile options] outfile}...

Use -h to get full help or, even better, run 'man ffmpeg'
```

Perhaps there is some way to fix the path it is searching manually?

```
On what OS are you running homebridge: Debian 10
On what iOS version are you having issues: iOS 13.7
What camera types are having issues: Google Hello
Does this issue occur consistently or randomly: Consistently
If applicable, what was the last version that worked properly: 
```
