Explicitly require rubygem(json).

rubygem-activesupport.spec

@@ -3,7 +3,7 @@
 Name: rubygem-%{gem_name}
 Epoch: 1
 Version: 5.1.3
-Release: 1%{?dist}
+Release: 2%{?dist}
 Summary: A support libraries and Ruby core extensions extracted from the Rails framework
 Group: Development/Languages
 License: MIT
@@ -17,9 +17,10 @@ Source0: https://rubygems.org/gems/%{gem_name}-%{version}.gem
 # git checkout v5.1.3 && tar czvf activesupport-5.1.3-tests.tgz test/
 Source1: %{gem_name}-%{version}-tests.tgz
 
-# ruby package has just soft dependency on rubygem(bigdecimal), while
-# ActiveSupport always requires it.
+# ruby package has just soft dependency on rubygem({bigdecimal,json}), while
+# ActiveSupport always requires them.
 Requires: rubygem(bigdecimal)
+Requires: rubygem(json)
 
 # Let's keep Requires and BuildRequires sorted alphabeticaly
 BuildRequires: ruby(release)
@@ -95,6 +96,9 @@ popd
 %doc %{gem_instdir}/README.rdoc
 
 %changelog
+* Tue Aug 22 2017 Vít Ondruch <vondruch@redhat.com> - 1:5.1.3-2
+- Explicitly require rubygem(json).
+
 * Tue Aug 08 2017 Pavel Valena <pvalena@redhat.com> - 1:5.1.3-1
 - Update to Active Support 5.1.3.