Fix echomsg call

Echomsg is a command, not Vimscript function. Also, call takes function
name as first argument and other arguments as additional varargs.

Author: Deraen

rplugin/python3/deoplete/sources/acid.py

@@ -65,7 +65,7 @@ def on_init(self, context):
         if loaded:
             self.acid_sessions = SessionHandler()
         else:
-            self.vim.call('echom "Acid.nvim not found. Please install it."')
+            self.vim.command('echomsg "Acid.nvim not found. Please install it."')
         self.sessions = {}
 
     def get_wc(self, url):