Update ShaderMaterial.html

Example code should be in a `code` element.

docs/api/materials/ShaderMaterial.html

@@ -25,6 +25,8 @@
 		<br>
 		Example:<br>
 		<br>
+		<pre>
+		<code>
 		uniforms = {
 			time: { type: "f", value: 1.0 },
 			resolution: { type: "v2", value: new THREE.Vector2() }
@@ -37,6 +39,8 @@
 			fragmentShader: document.getElementById( 'fragmentShader' ).textContent
 
 		} );
+		</code>
+		</pre>
 
 		</div>