Replace use of 'content' with 'title_content'

We'll only be modifying the subtitle and title, so use the provided
content templates.

lib/DDG/Goodie/RgbColor.pm

@@ -50,7 +50,7 @@ handle query_lc => sub {
             templates => {
                 group   => "text",
                 options => {
-                    content => 'DDH.rgb_color.content',
+                    title_content    => 'DDH.rgb_color.title_content',
                 },
             }
         };

t/RgbColor.t

@@ -22,7 +22,7 @@ sub build_structured_answer {
             templates => {
                 group   => "text",
                 options => {
-                    content => 'DDH.rgb_color.content',
+                    title_content => 'DDH.rgb_color.title_content',
                 },
             }
         };