patch 8.0.0180: error E937 is used twice

Problem:    Error E937 is used both for duplicate key in JSON and for trying
            to delete a buffer that is in use.
Solution:   Rename the JSON error to E938. (Norio Takagi, closes #1376)

Author: brammool

src/json.c

@@ -936,7 +936,7 @@ json_decode_item(js_read_T *reader, typval_T *res, int options)
 			&& dict_find(top_item->jd_tv.vval.v_dict,
 						 top_item->jd_key, -1) != NULL)
 		{
-		    EMSG2(_("E937: Duplicate key in JSON: \"%s\""),
+		    EMSG2(_("E938: Duplicate key in JSON: \"%s\""),
 							     top_item->jd_key);
 		    clear_tv(&top_item->jd_key_tv);
 		    clear_tv(cur_item);

src/testdir/test_json.vim

@@ -152,7 +152,7 @@ func Test_json_decode()
   call assert_fails('call json_decode("blah")', "E474:")
   call assert_fails('call json_decode("true blah")', "E488:")
   call assert_fails('call json_decode("<foobar>")', "E474:")
-  call assert_fails('call json_decode("{\"a\":1,\"a\":2}")', "E937:")
+  call assert_fails('call json_decode("{\"a\":1,\"a\":2}")', "E938:")
 
   call assert_fails('call json_decode("{")', "E474:")
   call assert_fails('call json_decode("{foobar}")', "E474:")

src/version.c

@@ -764,6 +764,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    180,
 /**/
     179,
 /**/