Drop 3.5 (support ended) and add 3.9

Author: yarikoptic

.travis.yml

@@ -1,10 +1,10 @@
 # vim ft=yaml
 language: python
 python:
-  - 3.5
   - 3.6
   - 3.7
   - 3.8
+  - 3.9
 
 cache:
   - apt

heudiconv/info.py

@@ -12,13 +12,14 @@
     'Environment :: Console',
     'Intended Audience :: Science/Research',
     'License :: OSI Approved :: Apache Software License',
-    'Programming Language :: Python :: 3.5',
     'Programming Language :: Python :: 3.6',
     'Programming Language :: Python :: 3.7',
+    'Programming Language :: Python :: 3.8',
+    'Programming Language :: Python :: 3.9',
     'Topic :: Scientific/Engineering'
 ]
 
-PYTHON_REQUIRES = ">=3.5"
+PYTHON_REQUIRES = ">=3.6"
 
 REQUIRES = [
     'nibabel',