tap-new: fix symlink creation.

Ensure the full HOMEBREW_TAP_DIR path is created before deleting and
creating the symlink for it. This ensures that non-`homebrew` taps will
have the necessary username/organisation folder created.

Fixes #2378.

Library/Homebrew/dev-cmd/tap-new.rb

@@ -60,6 +60,7 @@ module Homebrew
         - git -C "$HOMEBREW_REPOSITORY" reset --hard origin/master
         - brew update || brew update
         - HOMEBREW_TAP_DIR="$(brew --repo "$TRAVIS_REPO_SLUG")"
+        - mkdir -p "$HOMEBREW_TAP_DIR"
         - rm -rf "$HOMEBREW_TAP_DIR"
         - ln -s "$PWD" "$HOMEBREW_TAP_DIR"
         - export HOMEBREW_DEVELOPER="1"