fix: --unshallow errors if the repo is already unshallow

instead we use --depth=2147483647 because as noted by the docs...

  The special depth 2147483647 (or 0x7fffffff, the largest positive number a
  signed 32-bit integer can contain) means infinite depth.

  https://git-scm.com/docs/shallow

lua/dep/proc.lua

@@ -62,7 +62,7 @@ function proc.git_reset(dir, treeish, cb)
 end
 
 function proc.git_checkout(dir, branch, commit, cb)
-  local args = { "fetch", "--unshallow", "origin", branch }
+  local args = { "fetch", "--depth=2147483647", "origin", branch }
   proc.exec("git", args, dir, git_env, function(err, message)
     cb(err, message)