Use new shutdown procedure

The ycmd server has now a shutdown handler and we need to send a
shutdown request instead of killing the process.

See ycm-core/ycmd#282

Resolves abingham#240

ycmd.el

@@ -610,26 +610,29 @@ control.) The newly started server will have a new HMAC secret."
 
   (ycmd--start-keepalive-timer))
 
+(defun ycmd--shutdown ()
+  "Send a shutdown request to the server."
+  (ycmd--request "/shutdown" nil :parser 'json-read))
+
 (defun ycmd-close (&optional time-out-secs)
   "Shutdown any running ycmd server.
 
-Wait TIME-OUT-SECS seconds after `interrupt-process' call for the
-ycmd server to end before killing the process with
-`delete-process'.
+Wait TIME-OUT-SECS seconds after a shutdown request for the ycmd
+server to end before killing the process with `delete-process'.
 
 This does nothing if no server is running."
   (interactive)
 
-  (unwind-protect
-      (when (ycmd-running?)
-        (condition-case nil
-            (progn
-              (interrupt-process ycmd--server-process)
-              (when time-out-secs
-                (sit-for time-out-secs)
-                (delete-process ycmd--server-process)))
-          (error nil))
-        (ycmd--global-teardown)))
+  (when (ycmd-running?)
+    (unwind-protect
+        (progn
+          (ycmd--shutdown)
+          (when time-out-secs
+            (sit-for time-out-secs)
+            (condition-case nil
+                (delete-process ycmd--server-process)
+              (error nil))))
+      (ycmd--global-teardown)))
 
   (ycmd--kill-timer ycmd--keepalive-timer))