HTTP/2: fixed $server_protocol value (ticket #800).

src/http/v2/ngx_http_v2.c

diff --git a/src/http/v2/ngx_http_v2.c b/src/http/v2/ngx_http_v2.c
index bf07997..9c6aeb7 100644
--- a/src/http/v2/ngx_http_v2.c
+++ b/src/http/v2/ngx_http_v2.c
@@ -2762,6 +2762,8 @@
         return NULL;
     }
 
+    ngx_str_set(&r->http_protocol, "HTTP/2.0");
+
     r->http_version = NGX_HTTP_VERSION_20;
     r->valid_location = 1;