Update Python dependencies

Author: mdmintz

requirements.txt

@@ -36,7 +36,8 @@ msedge-selenium-tools==3.141.3
 more-itertools==5.0.0;python_version<"3.5"
 more-itertools==8.10.0;python_version>="3.5"
 cssselect==1.1.0
-filelock==3.2.0
+filelock==3.2.1;python_version<"3.6"
+filelock==3.3.0;python_version>="3.6"
 fasteners==0.16;python_version<"3.5"
 fasteners==0.16.3;python_version>="3.5"
 execnet==1.9.0
@@ -108,7 +109,8 @@ pdfminer.six==20201018;python_version>="3.5"
 # --- Testing Requirements --- #
 # ("pip install -r requirements.txt" also installs this, but "pip install -e ." won't.)
 
-coverage==5.5
+coverage==5.5;python_version<"3.6"
+coverage==6.0;python_version>="3.6"
 pytest-cov==2.12.1
 flake8==3.7.9;python_version<"3.5"
 flake8==3.9.2;python_version>="3.5"

setup.py

@@ -152,7 +152,8 @@
         'more-itertools==5.0.0;python_version<"3.5"',
         'more-itertools==8.10.0;python_version>="3.5"',
         "cssselect==1.1.0",
-        "filelock==3.2.0",
+        'filelock==3.2.1;python_version<"3.6"',
+        'filelock==3.3.0;python_version>="3.6"',
         'fasteners==0.16;python_version<"3.5"',
         'fasteners==0.16.3;python_version>="3.5"',
         "execnet==1.9.0",
@@ -224,7 +225,8 @@
     extras_require={
         # pip install -e .[coverage]
         "coverage": [
-            "coverage==5.5",
+            'coverage==5.5;python_version<"3.6"',
+            'coverage==6.0;python_version>="3.6"',
             "pytest-cov==2.12.1",
         ],
         # pip install -e .[flake]