CI: Build docker images with Python 3.8

Author: effigies

docker/generate_dockerfiles.sh

@@ -87,7 +87,7 @@ function generate_main_dockerfile() {
     --label maintainer="The nipype developers https://github.com/nipy/nipype" \
     --env MKL_NUM_THREADS=1 \
           OMP_NUM_THREADS=1 \
-    --arg PYTHON_VERSION_MAJOR=3 PYTHON_VERSION_MINOR=6 BUILD_DATE VCS_REF VERSION \
+    --arg PYTHON_VERSION_MAJOR=3 PYTHON_VERSION_MINOR=8 BUILD_DATE VCS_REF VERSION \
     --user neuro \
     --workdir /home/neuro \
     --miniconda create_env=neuro \