Add support for http2 directive

The new http2 directive obsoletes the http2
parameter of the listen directive which is
now deprecated.

https://docs.nginx.com/nginx/releases/#nginxplusrelease-30-r30

http://nginx.org/en/docs/http/ngx_http_v2_module.html#http2

Author: puneetsarna

analyze.go

@@ -698,6 +698,9 @@ var directives = map[string][]uint{
 	"http": {
 		ngxMainConf | ngxConfBlock | ngxConfNoArgs,
 	},
+	"http2": {
+		ngxHTTPMainConf | ngxHTTPSrvConf | ngxConfFlag,
+	},
 	"http2_body_preread_size": {
 		ngxHTTPMainConf | ngxHTTPSrvConf | ngxConfTake1,
 	},