build(deps): update actions/cache requirement to v2.1.5

Updates the requirements on [actions/cache](https://github.com/actions/cache) to permit the latest version.
- [Release notes](https://github.com/actions/cache/releases)
- [Commits](https://github.com/actions/cache/commits/1a9e2138d905efd099035b49d8b7a3888c653ca8)

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

.github/workflows/blog.yaml

@@ -16,7 +16,7 @@ jobs:
           # submodules: true  # Fetch Hugo themes (true OR recursive)
           fetch-depth: 3
       - name: Cache Conda
-        uses: actions/cache@v1
+        uses: actions/cache@v2.1.5
         with:
           path: ~/conda_pkgs_dir
           key: ${{ runner.os }}-conda6-${{ hashFiles('environment.yml') }}
@@ -42,7 +42,7 @@ jobs:
         run: |
           Rscript ./dependencies.R
       - name: Restore Blogdown Cache
-        uses: actions/cache@v2
+        uses: actions/cache@v2.1.5
         with:
           path: |
             ./blogdown
@@ -65,7 +65,7 @@ jobs:
       - uses: actions/setup-node@v1
         with:
           node-version: "12"
-      - uses: actions/cache@v2
+      - uses: actions/cache@v2.1.5
         with:
           path: ~/.npm
           key: ${{ runner.os }}-node-${{ hashFiles('**/package-lock.json') }}

.github/workflows/ci.yaml

@@ -14,7 +14,7 @@ jobs:
       - uses: actions/[email protected]
         with:
           node-version: "14"
-      - uses: actions/cache@v2
+      - uses: actions/cache@v2.1.5
         with:
           path: ~/.npm
           key: ${{ runner.os }}-node3-${{ hashFiles('**/package-lock.json') }}

.github/workflows/release_main.yml

@@ -47,7 +47,7 @@ jobs:
         with:
           node-version: "14"
       - name: Cache Node.js modules
-        uses: actions/cache@v2
+        uses: actions/cache@v2.1.5
         with:
           path: ~/.npm # npm cache files are stored in `~/.npm` on Linux/macOS
           key: ${{ runner.OS }}-node2-${{ hashFiles('**/package-lock.json') }}