Merge pull request #14709 from davidak/caddy-go16

caddy: build only with go 1.6

pkgs/top-level/all-packages.nix

···
 
   cabal2nix = self.haskellPackages.cabal2nix;
 
-  caddy = goPackages.caddy.bin // { outputs = [ "bin" ]; };
+  caddy = go16Packages.caddy.bin // { outputs = [ "bin" ]; };
 
   capstone = callPackage ../development/libraries/capstone { };
 
···
   cpulimit = callPackage ../tools/misc/cpulimit { };
 
   contacts = callPackage ../tools/misc/contacts { };
-  
+
   daemontools = callPackage ../tools/admin/daemontools { };
 
   datamash = callPackage ../tools/misc/datamash { };

pkgs/top-level/go-packages.nix

···
       acme blackfriday crypto go-humanize go-shlex go-syslog
       http-authentication lumberjack-v2 toml websocket yaml-v2
     ];
+    disabled = isGo14 || isGo15;
   };
 
   cascadia = buildGoPackage rec {