patch 9.0.1487: Content-type header for LSP channel not according to spec

Problem:    Content-type header for LSP channel not according to spec.
Solution:   Use "vscode-jsonrpc" instead of "vim-jsonrpc". (Yegappan
            Lakshmanan, closes #12295)
diff --git a/src/testdir/test_channel.vim b/src/testdir/test_channel.vim
index a6b25c9..6be2137 100644
--- a/src/testdir/test_channel.vim
+++ b/src/testdir/test_channel.vim
@@ -2670,7 +2670,7 @@
   " " Test for sending a raw message
   " let g:lspNotif = []
   " let s = "Content-Length: 62\r\n"
-  " let s ..= "Content-Type: application/vim-jsonrpc; charset=utf-8\r\n"
+  " let s ..= "Content-Type: application/vscode-jsonrpc; charset=utf-8\r\n"
   " let s ..= "\r\n"
   " let s ..= '{"method":"echo","jsonrpc":"2.0","params":{"m":"raw-message"}}'
   " call ch_sendraw(ch, s)