Fix using symbol on Element#attribute alwas getting nil

lib/oga/xml/element.rb

@@ -64,14 +64,14 @@ module Oga
       #
       # @return [Oga::XML::Attribute]
       def attribute(name)
-        if html?
-          ns = nil
+        name_str, ns = if html?
+          [name.to_s, nil]
         else
-          name, ns = split_name(name)
+          split_name(name)
         end
 
         attributes.each do |attr|
-          return attr if attribute_matches?(attr, ns, name)
+          return attr if attribute_matches?(attr, ns, name_str)
         end
 
         return
@@ -115,10 +115,10 @@ module Oga
         if found
           found.value = value
         else
-          name, ns = split_name(name)
+          name_str, ns = split_name(name)
 
           attr = Attribute.new(
-            :name           => name,
+            :name           => name_str,
             :namespace_name => ns,
             :value          => value
           )

spec/oga/xml/element_spec.rb

@@ -107,13 +107,23 @@ describe Oga::XML::Element do
     end
 
     describe 'using an HTML document' do
-      it 'returns an attribute containing a namespace separator' do
-        attr = Oga::XML::Attribute.new(:name => 'foo:bar', :value => 'foo')
-        el   = described_class.new(:name => 'foo', :attributes => [attr])
-        doc  = Oga::XML::Document.new(:children => [el], :type => :html)
+      let!(:attr) do
+        Oga::XML::Attribute.new(:name => 'foo:bar', :value => 'foo')
+      end
+      let!(:el) do
+        described_class.new(:name => 'foo', :attributes => [attr])
+      end
+      let!(:doc) do
+        Oga::XML::Document.new(:children => [el], :type => :html)
+      end
 
+      it 'returns an attribute with a name containing a namespace separator' do
         el.attribute('foo:bar').should == attr
       end
+
+      it 'returns an attribute with a name containing a namespace separator when using a Symbol' do
+        el.attribute(:'foo:bar').should == attr
+      end
     end
   end