change imgui shader

imgui.glsl

precision highp float;
layout (location = 0) in vec2 Position;
layout (location = 1) in vec2 UV;
layout (location = 2) in vec4 Color;
uniform mat4 ProjMtx;
out vec2 Frag_UV;
out vec4 Frag_Color;
void main()
{
    Frag_UV = UV;
    Frag_Color = vec4(pow(Color.rgb, vec3(2.2)), Color.a);;
    gl_Position = ProjMtx * vec4(Position.xy,0,1);
}