Update INSTALL.md (#5376)

Fix the bug according to Windows branch regulation

Author: vongosling

INSTALL.md

@@ -289,7 +289,7 @@ apt-get install flex bison libssl-dev libelf-dev dwarves bc
 
 First, you will need to checkout the WSL2 Linux kernel git repository:
 ```
-KERNEL_VERSION=$(uname -r | cut -d '-' -f 1)
+KERNEL_VERSION=$(uname -r | cut -d '.' -f 1-2 | xargs -I {} echo "{}.y")
 git clone --depth 1 https://github.com/microsoft/WSL2-Linux-Kernel.git -b linux-msft-wsl-$KERNEL_VERSION
 cd WSL2-Linux-Kernel
 ```