Improve test for adding idPrefix to xlink:href

While adding more things to this test, I noticed that the assertion for
idPrefix insertion in xlink:href attributes was lacking the actual
prefix. Adding it should make this bit of code more robust, which is
nice because I'm about to make some changes.

tests/svg-inline-loader.test.js

@@ -59,7 +59,7 @@ describe('getExtractedSVG()', function(){
 
         assert.isTrue( processedStyleInsertedSVG.match(/test\.prefix-foo/g).length === 3 );
         // // replaces xlink:href=
-        assert.isTrue( processedStyleInsertedSVG.match(/xlink:href=/g).length === 1 );
+        assert.isTrue( processedStyleInsertedSVG.match(/xlink:href="#test.prefix-foo"/g).length === 1 );
         // // replaces url(#foo)
         assert.isTrue( processedStyleInsertedSVG.match(/url\(#test\.prefix-foo\)/g).length === 1 );
     });