Correct translation calculation in recomposition of decomposed transform

As far as I can tell, this calculation for recomposing the transform is incorrect.

If you apply the given pseudocode description of decomposing and recomposing to the following matrix:

```
[ 1 1 10
  0 1 20 ]
```

Then you'd expect to get back the same matrix (decompose & recompose should be inverse functions).

However, if you follow the specification as given, then you get back something else.

Author: jlfwong

css-transforms-1/Overview.bs

@@ -1346,8 +1346,8 @@ matrix[1][0] = m21
 matrix[1][1] = m22
 
 // Translate matrix.
-matrix[3][0] = translate[0] * m11 + translate[1] * m21
-matrix[3][1] = translate[0] * m12 + translate[1] * m22
+matrix[3][0] = translate[0]
+matrix[3][1] = translate[1]
 
 // Rotate matrix.
 angle = deg2rad(angle);