Bump matplotlib from 3.6.1 to 3.7.1 in /rastervision_pytorch_learner

Bumps [matplotlib](https://github.com/matplotlib/matplotlib) from 3.6.1 to 3.7.1.
- [Release notes](https://github.com/matplotlib/matplotlib/releases)
- [Commits](matplotlib/matplotlib@v3.6.1...v3.7.1)

---
updated-dependencies:
- dependency-name: matplotlib
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

rastervision_pytorch_learner/requirements.txt

@@ -12,7 +12,7 @@ psutil==5.9.3
 triangle==20220202
 opencv-python==4.6.0.66
 opencv-python-headless==4.6.0.66
-matplotlib==3.6.1
+matplotlib==3.7.1
 tqdm==4.64.1
 onnx==1.14.0
 onnxruntime-gpu==1.15.0