docker-compose: rename from docker_compose, python3 by default

The command is called docker-compose hence the package should be called the same.
Also prefer python3.

pkgs/top-level/aliases.nix

@@ -85,6 +85,7 @@ mapAliases ({
   docbook5_xsl = docbook_xsl_ns; # added 2018-04-25
   docbook_xml_xslt = docbook_xsl; # added 2018-04-25
   double_conversion = double-conversion; # 2017-11-22
+  docker_compose = docker-compose; # 2018-11-10
   dwarf_fortress = dwarf-fortress; # added 2016-01-23
   emacsMelpa = emacs25PackagesNg; # for backward compatibility
   emacsPackagesGen = emacsPackagesFor; # added 2018-08-18

pkgs/top-level/all-packages.nix

@@ -154,7 +154,7 @@ with pkgs;
 
   dockerTools = callPackage ../build-support/docker { };
 
-  docker_compose = pythonPackages.docker_compose;
+  docker-compose = python3Packages.callPackage ../applications/virtualization/docker-compose {};
 
   docker-ls = callPackage ../tools/misc/docker-ls { };
 

pkgs/top-level/python-packages.nix

@@ -2222,8 +2222,6 @@ in {
 
   pyfribidi = callPackage ../development/python-modules/pyfribidi { };
 
-  docker_compose = callPackage ../development/python-modules/docker_compose {};
-
   pyftpdlib = callPackage ../development/python-modules/pyftpdlib { };
 
   fdroidserver = callPackage ../development/python-modules/fdroidserver { };