Update "optipng-bin" to version ~3.0.4

[marekventur]

3.0.4 / 2015-12-09

• 3.0.4
• ES2015ify readme
• Test on stable instead of iojs
• Remove unnecessary version check fix #58 fix #45
• Show more useful error message
• Use XO https://github.com/sindresorhus/xo

  3.0.3 / 2015-11-13

• 3.0.3
• Change version tag to include v As discussed in imagemin/gifsicle-bin#55, some imagemin bin packages prepend their version tags with v and some don't. This PR changes the behavior of this package to prepend tags withv, as do the majority of packages. This reduces the probability that a wrong tag is published by mistake. Merging this PR means that the next tag must be prepended with a v! Pull Request URL: https://github.com/imagemin/optipng-bin/pull/63
• Replace fs.exists with path-exists

  3.0.2 / 2015-06-06

• 3.0.2
• Fix URL

  3.0.1 / 2015-06-06

• 3.0.1
• Minor tweak

  3.0.0 / 2015-06-06

• 3.0.0
• minor package.json tweaks
• Use mocha for testing
• Export it directly
• Tweaks
• Bump bin-wrapper dependency
• Update .travis.yml