Fix docs deployment and bump python version (#22)

* chore(docs): update workflow

* chore(ci): bump python version from 3.8 to 3.9

.github/workflows/build-and-test.yml

@@ -16,7 +16,7 @@ jobs:
     - name: Set up Python
       uses: actions/setup-python@v2
       with:
-        python-version: "3.8"
+        python-version: "3.9"
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip

.github/workflows/deploy-docs.yml

@@ -11,10 +11,11 @@ jobs:
     steps:
       - uses: actions/checkout@v2
       - uses: actions/setup-python@v2
+        with:
+          python-version: "3.9"
       - name: Install dependencies
         run: |
           sudo apt install pandoc
-          pip install torch pennylane
           pip install -r requirements-dev.txt
       - name: Sphinx build
         run: |