wordpress: 4.7.4 -> 4.7.6

[pbogdan]

Motivation for this change

This is for 17.09.

Update to the most recent maintenance and security release in 4.7.x series:

• https://codex.wordpress.org/Version_4.7.5
• https://codex.wordpress.org/Version_4.7.6

Fixes broken test.

Not sure if such a version bump is appropriate for the stable release but submitting this on account of multiple security fixes included.

/cc @basvandijk

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option build-use-sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Fits CONTRIBUTING.md.

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[grahamc]

Yes, definitely appreciated. Thank you.