BUG: FIX travis error for python3.8

Update pytest to 5.4.2 to fix the above issue.

Author: shaneahmed

requirements_dev.txt

@@ -9,7 +9,7 @@ Sphinx==1.8.5
 twine==1.14.0
 Click==7.0
 setuptools==45.1.0
-pytest==4.6.5
+pytest==5.4.2
 pytest-runner==5.1
 opencv-python==4.2.0.34
 pathos==0.2.5

tests/test_tiatoolbox.py

@@ -62,7 +62,7 @@ def test_command_line_help_interface():
     assert help_result.output == result.output
 
 
-def test_command_line_slide_info():
+def test_command_line_slide_info(response_ndpi, response_svs):
     """Test the Slide infor CLI."""
     runner = CliRunner()
     slide_info_result = runner.invoke(