upgrade bin/pngquant for best reduced quality

[cofemei]

2.4.0

$ ./pngquant --version
2.4.0 (April 2015)
$./pngquant --force --quality=60-100 --verbose 1468407_42020359_004.png --output 1468407_42020359_004_90.png 
1468407_42020359_004.png:
  read 2496KB file
  made histogram...536779 colors found
  selecting colors...4%
  selecting colors...7%
  selecting colors...11%
  selecting colors...14%
  selecting colors...35%
  selecting colors...38%
  selecting colors...59%
  selecting colors...63%
  selecting colors...83%
  selecting colors...100%
  moving colormap towards local minimum
  image degradation MSE=13.391 (Q=59) exceeded limit of 13.237 (60)
Skipped 1 file out of a total of 1 file.

2.11.4

$ ./pngquant/pngquant --version
2.11.4 (November 2017)
$./pngquant/pngquant --force --quality=60-100 --verbose 1468407_42020359_004.png --output 1468407_42020359_004_90.png 
1468407_42020359_004.png:
  read 2496KB file
  made histogram...536779 colors found
  selecting colors...3%
  selecting colors...6%
  selecting colors...10%
  selecting colors...13%
  selecting colors...17%
  selecting colors...37%
  selecting colors...58%
  selecting colors...79%
  selecting colors...82%
  selecting colors...100%
  moving colormap towards local minimum
  eliminated opaque tRNS-chunk entries...0 entries transparent
  mapped image to new colors...MSE=6.781 (Q=77)
  writing 256-color image as 1468407_42020359_004_90.png
Quantized 1 image.