[BugFix] Remove strict coverage requirement from setup.py (#373)

Author: gchhablani

setup.py

@@ -33,7 +33,7 @@ def run_tests(self):
     exec(version_file.read(), package_config)
 
 tests_require = [
-    "coverage==4.5.4",
+    "coverage",
     "coveralls==1.3.0",
     "flake8==3.0.4",
     "pytest==3.5.1",