Update ccShader_PositionTextureColor_frag.h

gray scale mode test, if ypuo want  colorful mode comment the following code.
float luminance = (gl_FragColor.r*0.3 + gl_FragColor.g*0.59 + gl_FragColor.b*0.11);                \n\
    	gl_FragColor =  vec4(luminance, luminance, luminance, gl_FragColor.a);			\n\