[luacheck] openresty provides coroutine._* methods

.luacheckrc

@@ -1,8 +1,18 @@
-std = 'ngx_lua+lua52' -- lua52 has table.pack
+local standards = require "luacheck.standards"
+
+-- stds global is provided by luacheck
+-- https://luacheck.readthedocs.io/en/stable/config.html#custom-sets-of-globals
+stds.ngx = {
+    read_globals = {
+        coroutine = standards.def_fields('_yield', '_create', '_resume')
+    }
+}
+
+std = 'ngx_lua+lua52+ngx' -- lua52 has table.pack
 
 busted = {std = "+busted", globals = { 'fixture' } }
 files["**/spec/**/*_spec.lua"] = busted
 
 globals = { 'rawlen' }
 
-files['gateway/config/*.lua'] = { globals = { 'context' } }
+files['gateway/config/*.lua'] = { globals = { 'context' } }