Update install.sh

Release v0.2.1

Fixing #37 where file url update caused 1.20 to be missing

v0.2.0

Adds support for listing installed versions
Adds support for removing a specific version
Adds supoprt for cleaning off inactive versions
Adds support for GOROOT_BOOTSTRAP
General Cleanup
Corrects issues with autoupdate release process

Version v0.1.1

Version v0.1.0

This version introduces logic which allows `gvm` to identify
if there are newer versions of a released instance and gives
the user the option to update the script.

This version also introduces versions which will be displayed
in the help text of `gvm`.

The linking has also changed so that `gvm` correctly links the
entire `go` directory and not just the `bin` directory.

Version v0.0.5

Version v0.0.4

Version v0.0.3

Version v0.0.2