build: update next branch to reflect new release-train `v12.0.0-next.0`
build: update next branch to reflect new release-train `v12.0.0-next.0`

This is needed as otherwise the ng-dev tools will fail due to `Error: Discovered unexpected version-branch "11.2.x" for a release-train that is already active in the "master" branch. Please either delete the branch if created by accident, or update the version in the next branch (master).`

ocombe/angular-cli,Brocco/angular-cli,catull/angular-cli,angular/angular-cli,catull/angular-cli,catull/angular-cli,clydin/angular-cli,ocombe/angular-cli,ocombe/angular-cli,clydin/angular-cli,clydin/angular-cli,geofffilippi/angular-cli,Brocco/angular-cli,clydin/angular-cli,catull/angular-cli,angular/angular-cli,Brocco/angular-cli,ocombe/angular-cli,angular/angular-cli,geofffilippi/angular-cli,Brocco/angular-cli,geofffilippi/angular-cli,ocombe/angular-cli,geofffilippi/angular-cli,angular/angular-cli,Brocco/angular-cli