Allow npm install of spago@next

[natefaubion]

Currently spago is hardcoded to use github releases for legacy spago. Would it be possible to use npm for install for spago next/unstable?

[natefaubion]

Current workaround is to install spago in a step using npm and invoke from node_modules/.bin or npx.

[thomashoneyman]

Yes, we would need to update this:

setup-purescript/src/Setup/Data/Tool.purs

Lines 118 to 133 in b059776

	Spago -> Tarball
	{ source: formatGitHub'
	-- Spago has changed naming conventions from version to version
	if version >= unsafeVersion "0.18.1" then case platform of
	Windows -> "Windows"
	Mac -> "macOS"
	Linux -> "Linux"
	else if version == unsafeVersion "0.18.0" then case platform of
	Windows -> "windows-latest"
	Mac -> "macOS-latest"
	Linux -> "linux-latest"
	else case platform of
	Windows -> "windows"
	Mac -> "osx"
	Linux -> "linux"
	, getExecutablePath: \p -> Path.concat [ p, executableName ]

...such that if the Spago version is greater than 0.90.x then we use NPM as the installation method.

[thomashoneyman]

We would also need to update the get latest versions script so that it looks at NPM releases for Spago; right now everything looks at GitHub releases, but the spago@next releases are not happening on GitHub releases at all.

setup-purescript/src/Setup/UpdateVersions.purs

Line 74 in b059776

Spago -> fetchFromGitHubReleases