Change drone to run one version of py3 and py2 for testing. Needed to specify pytest versions depending on if above or below python version 3.

.drone.yml

@@ -8,8 +8,8 @@ platform:
   arch: amd64
 
 steps:
-- name: test-python3.6
-  image: python:3.6-alpine
+- name: test-python2.7
+  image: python:2.7-alpine
   commands:
   - python --version
   - pip install -r requirements.txt
@@ -23,7 +23,7 @@ steps:
   - py.test
 
 - name: codecov
-  image: python:3.6-alpine
+  image: python:3.8-alpine
   environment:
     CODECOV_TOKEN:
       from_secret: CODECOV_TOKEN

requirements.txt

@@ -5,5 +5,6 @@ enzyme>=0.4.1
 click>=6.7
 langdetect>=1.0.7
 titlecase>=0.12.0
-pytest>=5.3.5
+pytest>=4.6.9 ; python_version <= '2.7'
+pytest>=5.3.5 ; python_version > '2.7'
 pytest-cov>=2.8.1