fixed a couple of issues that made the notebook not work in colab (#1460)

* fixed a couple of issues that made the notebook not work in colab

i fixed a couple of issues that made the notebook not work in colab 
1. it downloaded incompatible versions of pytorch and cuda + the conda command doesnt do anything in colab since there is no conda in colab idk w y wanna do about that - The commit of 2 days ago only changes the conda command version and not the pip command which is used while isntaling mcvv
2. /demo.png doesnt exist in colab so i added a wget to download some cityscapes photo from the internet and run inference on that photo
3. i think it would be optimal to have 2 notebooks. 1 for running locally when cloning your git branch and one to run in google colab.

* Update demo/MMSegmentation_Tutorial.ipynb

* Update demo/MMSegmentation_Tutorial.ipynb

* Update demo/MMSegmentation_Tutorial.ipynb

* Update demo/MMSegmentation_Tutorial.ipynb

* Update demo/MMSegmentation_Tutorial.ipynb

Co-authored-by: Miao Zheng <76149310+MeowZheng@users.noreply.github.com>