fix typo (#431)

* fix typo

* fix typo

Author: afilahkle

webgl/lessons/webgl-3d-orthographic.md

@@ -346,7 +346,7 @@ units as well.  I'll pass in some value similar to `width` for the `depth`
 so our space will be 0 to `width` pixels wide, 0 to `height` pixels tall, but
 for `depth` it will be `-depth / 2` to `+depth / 2`.
 
-Finally we need to to update the code that computes the matrix.
+Finally we need to update the code that computes the matrix.
 
 ```
   // Compute the matrix

webgl/lessons/webgl-qna-pure-webgl-dashed-line.md

@@ -41,7 +41,7 @@ I'm assuming it works like this. You have a buffer of positions. You make a corr
       lengthSoFar.push(lengthSoFar[ii - 1] + distance(positions, ii - 1, ii));
     }
 
-Now you can make buffers for both `positions` and `lengthSoFar` and pass `lengthSoFar` as an attribute into your vertex shader and from there pass it as a varying to to your fragment shader.
+Now you can make buffers for both `positions` and `lengthSoFar` and pass `lengthSoFar` as an attribute into your vertex shader and from there pass it as a varying to your fragment shader.
 
 Unfortunately it won't work with indexed geometry (the most common type?). In other words it won't work with `gl.drawElements`, only with `gl.drawArrays`. Also the dashed line would be dashed in 3D not 2D so a line going into the screen (away from the viewer) would look different than a line going across the screen. Of course if you're drawing 2D then there's no problem.