Bump pytest-sugar to v0.9.3

Ref: Teemu/pytest-sugar#188 (comment)

setup.cfg

@@ -86,7 +86,7 @@ docs =
 testing =
     pytest>=4.6.6
     pytest-mock>=1.11.0
-    pytest-sugar>=0.9.1
+    pytest-sugar>=0.9.3
     pytest-testmon<1.0.0
     pytest-watch==4.2.0
     pytest-xdist>=1.28.0