Fix link for GraphPrinter

GraphPrinter went to GraphHtmlPrinter instead

Author: costi

index.html

@@ -428,7 +428,7 @@ <h2><a id="reports">Reports</a></h2>
                 a good way of quickly identifying which methods take the most time.
                 An example of a flat report can be found in <a href="./examples/primes.flat.txt">examples/primes.flat.txt</a>.
             </dd>
-            <dt>Graph Reports (<a href="doc/RubyProf/GraphHtmlPrinter.html">RubyProf::GraphPrinter</a>)</dt>
+            <dt>Graph Reports (<a href="doc/RubyProf/GraphPrinter.html">RubyProf::GraphPrinter</a>)</dt>
             <dd>The graph report shows the overall time spent in each method. In
                 addition, it also show which methods call the current method and
                 which methods its calls. Thus they are good for understanding how