Tests: grpc module prerequisite.

lib/Test/Nginx.pm

diff --git a/lib/Test/Nginx.pm b/lib/Test/Nginx.pm
index b51b8b6..b4472b9 100644
--- a/lib/Test/Nginx.pm
+++ b/lib/Test/Nginx.pm
@@ -139,6 +139,7 @@
 		fastcgi	=> '(?s)^(?!.*--without-http_fastcgi_module)',
 		uwsgi	=> '(?s)^(?!.*--without-http_uwsgi_module)',
 		scgi	=> '(?s)^(?!.*--without-http_scgi_module)',
+		grpc	=> '(?s)^(?!.*--without-http_grpc_module)',
 		memcached
 			=> '(?s)^(?!.*--without-http_memcached_module)',
 		limit_conn