vim-patch:8.1.0542: shiftwidth() does not take 'vartabstop' into account

Problem:    shiftwidth() does not take 'vartabstop' into account.
Solution:   Use the cursor position or a position explicitly passed.
            Also make >> and << work better with 'vartabstop'. (Christian
            Brabandt)
f951416a83

src/nvim/eval.lua

@@ -309,7 +309,7 @@ return {
     setwinvar={args=3},
     sha256={args=1},
     shellescape={args={1, 2}},
-    shiftwidth={},
+    shiftwidth={args={0, 1}},
     sign_define={args={1, 2}},
     sign_getdefined={args={0, 1}},
     sign_getplaced={args={0, 2}},