fix: typo

Author: 태재영

webgl/lessons/webgl-drawing-without-data.md

@@ -604,5 +604,5 @@ So, if either of those issues is a problem for your needs then as a solution you
 with <code>gl.TRIANGLES</code> instead of using <code>gl.POINTS</code>.
  If you do that both problems are solved.
 The maximum size problem goes away as does the inconsistent clipping problem. There are various
-ways to draw lots of quads. One of then is using techniques like the ones in this article.</p>
+ways to draw lots of quads. One of them is using techniques like the ones in this article.</p>
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