Merge pull request #412 from stac-utils/dependabot/pip/coverage-eq-5.5

Update coverage requirement from ==5.2.* to ==5.5

Author: Jon Duckworth

requirements-test.txt

@@ -6,7 +6,7 @@ codespell==1.17.1
 
 jsonschema==3.2.0
 pylint==1.9.1
-coverage==5.2.*
+coverage==5.5
 doc8==0.8.1
 
 # optional dependencies