Flag to fix std version

[TomokiMiyauci]

There are cases where you want to specify the version of deno.land/std module.

For example, deno 1.17.0 has been replaced by TypeScript 4.5, which supports type modifier on individual named imports.

In environments where this is not supported (e.g. [email protected]), you may want to use [email protected].

deno	std
1.17.0	0.118.0
1.16.4	0.117.0

I understand this is an edge case, what do you think of this feature?