complete: fix off by one

Fix off by one in column calculation introduced in #3617.

Fixes #3625

autoload/go/complete.vim

@@ -24,7 +24,7 @@ function! go#complete#Complete(findstart, base) abort
   "findstart = 1 when we need to get the start of the match
   if a:findstart == 1
     let [l:line, l:col] = getpos('.')[1:2]
-    let [l:line, l:col] = go#lsp#lsp#Position(l:line, l:col)
+    let [l:line, l:col] = go#lsp#lsp#Position(l:line, l:col-1)
     let l:completion = go#lsp#Completion(expand('%:p'), l:line, l:col, funcref('s:handler', [l:state]))
     if l:completion
       return -3