Add missing BuildRequires on gcc

make: gcc: Command not found

References: https://bugzilla.redhat.com/show_bug.cgi?id=1606247
Signed-off-by: Igor Gnatenko <ignatenkobrain@fedoraproject.org>

rubygem-redcarpet.spec

@@ -9,6 +9,7 @@ Group: Development/Languages
 License: MIT and ISC
 URL: http://github.com/vmg/redcarpet
 Source0: https://rubygems.org/gems/%{gem_name}-%{version}.gem
+BuildRequires:  gcc
 BuildRequires: ruby(release)
 BuildRequires: rubygems-devel
 BuildRequires: ruby-devel