add explicit BR for the gcc-c++ compiler

... as instructed at:

https://fedoraproject.org/wiki/Packaging:C_and_C%2B%2B

nghttp2.spec

@@ -1,7 +1,7 @@
 Summary: Experimental HTTP/2 client, server and proxy
 Name: nghttp2
 Version: 1.30.0
-Release: 2%{?dist}
+Release: 3%{?dist}
 License: MIT
 Group: Applications/Internet
 URL: https://nghttp2.org/
@@ -9,6 +9,7 @@ Source0: https://github.com/tatsuhiro-t/nghttp2/releases/download/v%{version}/ng
 
 BuildRequires: CUnit-devel
 BuildRequires: c-ares-devel
+BuildRequires: gcc-c++
 BuildRequires: libev-devel
 BuildRequires: openssl-devel
 BuildRequires: systemd-devel
@@ -111,6 +112,9 @@ make %{?_smp_mflags} check
 
 
 %changelog
+* Mon Feb 19 2018 Kamil Dudka <kdudka@redhat.com> 1.30.0-3
+- add explicit BR for the gcc-c++ compiler
+
 * Thu Feb 08 2018 Fedora Release Engineering <releng@fedoraproject.org> - 1.30.0-2
 - Rebuilt for https://fedoraproject.org/wiki/Fedora_28_Mass_Rebuild