make $request_method non-cacheable

src/http/ngx_http_variables.c

diff --git a/src/http/ngx_http_variables.c b/src/http/ngx_http_variables.c
index 713df22..f3fc9f6 100644
--- a/src/http/ngx_http_variables.c
+++ b/src/http/ngx_http_variables.c
@@ -196,7 +196,8 @@
     { ngx_string("server_name"), NULL, ngx_http_variable_server_name, 0, 0, 0 },
 
     { ngx_string("request_method"), NULL,
-      ngx_http_variable_request_method, 0, 0, 0 },
+      ngx_http_variable_request_method, 0,
+      NGX_HTTP_VAR_NOCACHEABLE, 0 },
 
     { ngx_string("remote_user"), NULL, ngx_http_variable_remote_user, 0, 0, 0 },