Bump numpy from 1.19 to 1.21.0 in /doc (#124)

* Bump numpy from 1.19 to 1.21.0 in /doc

Bumps [numpy](https://github.com/numpy/numpy) from 1.19 to 1.21.0.
- [Release notes](https://github.com/numpy/numpy/releases)
- [Changelog](https://github.com/numpy/numpy/blob/main/doc/HOWTO_RELEASE.rst.txt)
- [Commits](numpy/numpy@v1.19.0...v1.21.0)

---
updated-dependencies:
- dependency-name: numpy
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

* Relax the version requirement and use Python 3.8 to build the documentation.

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Boxi Li <etamin1201@gmail.com>

.github/workflows/test.yml

@@ -40,7 +40,7 @@ jobs:
     - name: Set up Python
       uses: actions/setup-python@v2
       with:
-        python-version: 3.6
+        python-version: 3.8
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip
@@ -68,7 +68,7 @@ jobs:
     - name: Set up Python
       uses: actions/setup-python@v2
       with:
-        python-version: 3.6
+        python-version: 3.8
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip

doc/requirements.txt

@@ -1,11 +1,11 @@
-numpy==1.19
-scipy==1.5.3
-qutip==4.6.0
-cython==0.29.21
-sphinx==3.5.2
+numpy==1.21
+scipy==1.5
+qutip==4.6
+cython==0.29
+sphinx==3.5
 sphinx_rtd_theme==0.5.1
 readthedocs-sphinx-search==0.1.0rc3
-numpydoc==1.1.0
-matplotlib==3.3.4
+numpydoc==1.1
+matplotlib==3.3
 docutils==0.16
 sphinxcontrib-bibtex==2.4