Add missing BuildRequires on gcc

make: gcc: Command not found

References: https://bugzilla.redhat.com/show_bug.cgi?id=1606202
Signed-off-by: Igor Gnatenko <ignatenkobrain@fedoraproject.org>

rubygem-http_parser.rb.spec

@@ -13,6 +13,7 @@ Source0:	https://rubygems.org/gems/%{gem_name}-%{version}.gem
 # name. Patch aims to update them to the newer Expectations.
 Patch0:		http_parser.rb-0.6.0-rspec3.patch
 Patch1:		http_parser.rb-0.6.0-usr_bin_ruby.patch
+BuildRequires:  gcc
 BuildRequires:	rubygems-devel 
 BuildRequires:	ruby-devel 
 BuildRequires:	rubygem-rspec