Make playground CI checks more robust.

.github/workflows/playground.yml

@@ -25,31 +25,28 @@ jobs:
       uses: actions/cache@v2
       with:
         path: |
-          ~/.cabal
           ~/.stack
           ~/.stack-work
-          ~/.dist-newstyle
           ~/.ghc
-        key: ${{ runner.os }}-${{ hashFiles('**/*.cabal') }}-cache
+        key: ${{ runner.os }}-${{ hashFiles('**/*.cabal') }}-cache-version2
 
     - name: Install dependencies
       run: |
-        cabal v2-update
-        cabal v2-build --enable-coverage --only-dependencies
+        sudo apt-get -y install texlive texlive-latex-base texlive-latex-extra
+        stack build --only-dependencies
+        (cd playground && stack build --only-dependencies)
 
     - name: Build
       run: |
-        cabal v2-build --enable-coverage
+        stack build
+        (cd playground && stack build)
 
     - name: Playground
       run: |
-        sudo apt-get -y install texlive texlive-latex-base texlive-latex-extra
         CWD=`pwd`
-        stack build
         cd playground
-        stack build
         # We need to install latex before we can generate the snippets.
         stack exec --cwd ../ playground snippets playground/snippets > viewer-elm/dist/snippets.js
         cd viewer-elm
-        npm install
+        npm install || npm install || npm install
         npm run build