Update travis to actually use different Python versions

.travis.yml

@@ -3,14 +3,22 @@
 language: python
 python:
   # We don't actually use the Travis Python, but this keeps it organized.
-  - "3.5"
-  - "3.6"
   - "3.7"
   - "3.8"
+  - "3.9"
 install:
   - sudo apt update
   # We do this conditionally because it saves us some downloading if the
   # version is the same.
+  if [[ "$TRAVIS_PYTHON_VERSION" == "3.7" ]]; then
+      wget https://repo.continuum.io/miniconda/Miniconda3-py37_4.8.3-Linux-x86_64.sh -O miniconda.sh;
+  elif [[ "$TRAVIS_PYTHON_VERSION" == "3.8" ]]; then
+      wget https://repo.continuum.io/miniconda/Miniconda3-py38_4.9.2-Linux-x86_64.sh -O miniconda.sh;
+  elif [[ "$TRAVIS_PYTHON_VERSION" == "3.8" ]]; then
+      wget https://repo.continuum.io/miniconda/Miniconda3-py39_4.9.2-Linux-x86_64.sh -O miniconda.sh;
+  else
+      wget https://repo.continuum.io/miniconda/Miniconda3-latest-Linux-x86_64.sh -O miniconda.sh;
+  fi
   - wget https://repo.continuum.io/miniconda/Miniconda3-latest-Linux-x86_64.sh -O miniconda.sh;
   - bash miniconda.sh -b -p $HOME/miniconda
   - export PATH="$HOME/miniconda/bin:$PATH"