chore(cask): fix cask vs formula terminology

Homebrew casks are their own thing, separate from formulas. Hence remove
all mentions to "formula" to avoid confusion.

.github/workflows/update-casks.yml

@@ -0,0 +1,61 @@
+---
+name: Update Casks
+on:
+  schedule:
+    - cron: "0 3 * * *"
+  workflow_dispatch:
+    inputs:
+      extraArgs:
+        description: "Extra arguments passed to emacs-builder cask update"
+        required: false
+        default: ""
+
+jobs:
+  update-casks:
+    runs-on: macos-10.15
+    steps:
+      - name: Checkout tap repository
+        uses: actions/checkout@v2
+        with:
+          path: tap
+      - name: Symlink homebrew tap
+        run: |
+          mkdir -p "$(brew --repo)/Library/Taps/jimeh"
+          ln -s "${{ github.workspace }}/tap" \
+             "$(brew --repo)/Library/Taps/jimeh/homebrew-emacs-builds"
+      - name: brew livecheck
+        run: >-
+          brew livecheck --json --quiet --tap jimeh/emacs-builds
+          | tee livecheck-results.json
+      - name: Upload livecheck-results.json artifact
+        uses: actions/upload-artifact@v2
+        with:
+          name: livecheck-results.json
+          path: livecheck-results.json
+          if-no-files-found: error
+      - name: Checkout build-emacs-for-macos for emacs-builder tool
+        uses: actions/checkout@v2
+        with:
+          repository: jimeh/build-emacs-for-macos
+          ref: "v0.6.6"
+          path: builder
+      - uses: actions/setup-go@v2
+        with:
+          go-version: 1.16
+      - uses: actions/cache@v2
+        with:
+          path: ~/go/pkg/mod
+          key: ${{ runner.os }}-go-${{ hashFiles('builder/**/go.sum') }}
+          restore-keys: ${{ runner.os }}-go-
+      - name: Build emacs-builder tool
+        run: make build
+        working-directory: builder
+      - name: Update casks
+        run: >-
+          builder/bin/emacs-builder
+          cask --builds-repository jimeh/emacs-builds
+          update --templates-dir tap/templates
+          ${{ github.event.inputs.extraArgs }}
+          livecheck-results.json
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}