Shader cannot move texture x, y location
What you do is shifting the texture coordinates. This will move the texture on your polygon, and depending on your settings it will handle the borders which are now probably wrong. however, this will not move your polygon - if you want to move an entire object, you should not do that within the shader. you do that via modifying your model matrix.

I assume you have a rectangle, and you want to move it by 0.2 along the x axis. Then you would edit the correct element of your model matrix for the rectangle. 

//depending on your setup, you may need [0][3] rather than [3][0]
modelMatrix[3][0] += 0.2;
//now upload the matrix to your shader
//the entire object will be moved by 0.2 units 


If that is what you wanted, then you need to remove the fragment shader position calculation.

On a sidenote: I had problems with using += in a shader the other day, so it might just be that this doesn't compile. Try using position = position + 0.2; instead.