gopls/doc: update coc.nvim config

Language server config name is 'go'.

Change-Id: I6ed4f13f6214bd37b518e24e0d64cfbd6ebd635c
Reviewed-on: https://go-review.googlesource.com/c/tools/+/485835
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Hyang-Ah Hana Kim <hyangah@gmail.com>
gopls-CI: kokoro <noreply+kokoro@google.com>
Commit-Queue: Hyang-Ah Hana Kim <hyangah@gmail.com>
Run-TryBot: Hyang-Ah Hana Kim <hyangah@gmail.com>
Reviewed-by: Robert Findley <rfindley@google.com>
diff --git a/gopls/doc/vim.md b/gopls/doc/vim.md
index 1fa44bf..8be533c 100644
--- a/gopls/doc/vim.md
+++ b/gopls/doc/vim.md
@@ -91,7 +91,7 @@
 
 ```json
   "languageserver": {
-    "golang": {
+    "go": {
       "command": "gopls",
       "rootPatterns": ["go.work", "go.mod", ".vim/", ".git/", ".hg/"],
       "filetypes": ["go"],