HashWithIndifferent access for props threw

Now, conversion of props works for HashWithIndifferentAccess. Previously
crashed.

.travis.yml

@@ -37,9 +37,9 @@ before_install:
 
 install:
   - travis_retry gem install bundler
-  - travis_retry nvm install 9.11.1
+  - travis_retry nvm install 8.11.3
   - node -v
-  - travis_retry npm i -g yarn@0.27.5
+  - travis_retry npm i -g yarn
   - travis_retry yarn global add babel-cli
   - travis_retry bundle install
   - travis_retry yarn

lib/react_on_rails/react_on_rails_helper.rb

@@ -264,7 +264,7 @@ def server_render_js(js_expression, options = {})
 
     def json_safe_and_pretty(hash_or_string)
       return "{}" if hash_or_string.nil?
-      unless hash_or_string.class.in?([Hash, String])
+      unless hash_or_string.is_a?(String) || hash_or_string.is_a?(Hash)
         raise ReactOnRails::Error, "#{__method__} only accepts String or Hash as argument "\
             "(#{hash_or_string.class} given)."
       end

spec/dummy/Gemfile.lock

@@ -7,7 +7,7 @@ GIT
 PATH
   remote: ../..
   specs:
-    react_on_rails (11.0.6)
+    react_on_rails (11.0.7)
       addressable
       connection_pool
       execjs (~> 2.5)
@@ -350,4 +350,4 @@ DEPENDENCIES
   webpacker
 
 BUNDLED WITH
-   1.16.1
+   1.16.2

spec/dummy/spec/helpers/react_on_rails_helper_spec.rb

@@ -35,6 +35,16 @@
       expect { helper.json_safe_and_pretty(false) }.to raise_error
     end
 
+    it "should return empty json when an empty Hash" do
+      escaped_json = helper.json_safe_and_pretty({})
+      expect(escaped_json).to eq("{}")
+    end
+
+    it "should return empty json when an empty HashWithIndifferentAccess" do
+      escaped_json = helper.json_safe_and_pretty(HashWithIndifferentAccess.new)
+      expect(escaped_json).to eq("{}")
+    end
+
     it "should return empty json when nil" do
       escaped_json = helper.json_safe_and_pretty(nil)
       expect(escaped_json).to eq("{}")