zsh: vimscratch: add filetype arg

Allows setting filetype for vimscratch command.

Usage: `<command> | vimscratch [filetype]`.

For example:

```bash
curl https://myip.wtf/json | vimscratch json
```
Will open the output of the curl command as a json
temporary file in vim.

functions/vim.zsh

@@ -6,5 +6,13 @@ vimscratch() {
     if [ ! -t 0 ] ; then
         stdin_arg="-"
     fi
-    vim -c "set buftype=nofile" $@ $stdin_arg
+    set +x
+    if [[ -n "$1" ]]; then
+        filetype=$1
+        shift
+        vim -c "set buftype=nofile" -c "set filetype=$filetype" $@ $stdin_arg
+    else
+        vim -c "set buftype=nofile" $filetype_arg $@ $stdin_arg
+    fi
+
 }