Update equation src URL

Author: kgryte

lib/node_modules/@stdlib/math/special/abs/README.md

@@ -31,7 +31,7 @@ The [absolute value][absolute-value] is defined as
 <!-- <equation class="equation" label="eq:absolute_value" align="center" raw="|x| = \begin{cases} x & \textrm{if}\ x \geq 0 \\ -x & \textrm{if}\ x < 0\end{cases}" alt="Absolute value"> -->
 
 <div class="equation" align="center" data-raw-text="|x| = \begin{cases} x &amp; \textrm{if}\ x \geq 0 \\ -x &amp; \textrm{if}\ x &lt; 0\end{cases}" data-equation="eq:absolute_value">
-    <img src="" alt="Absolute value">
+    <img src="https://cdn.rawgit.com/stdlib-js/stdlib/61c5f878886bd5b3b98976501c974bf69f575238/lib/node_modules/@stdlib/math/special/abs/docs/img/equation_absolute_value.svg" alt="Absolute value">
     <br>
 </div>