Fix interfaces typo

public/interfaces

@@ -40,7 +40,7 @@ signatures.</p>
             
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-	        <a href="http://play.golang.org/p/vx8bwC-Bmq"><img title="Run code" src="play.png" class="run" /></a>
+	        <a href="http://play.golang.org/p/guxTzcucR-"><img title="Run code" src="play.png" class="run" /></a>
             <div class="highlight"><pre><span class="kn">package</span> <span class="nx">main</span>
 </pre></div>
 
@@ -172,7 +172,7 @@ to work on any <code>geometry</code>.</p>
             <p>The <code>circle</code> and <code>square</code> struct types both
 implement the <code>geometry</code> interface so we can use
 instances of
-these structs as arguments to measure.</p>
+these structs as arguments to <code>measure</code>.</p>
 
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