Attempting to exclude lines that we can't necessarily hit in tests, added a test, fixed function name

update_profile_background_image has been in endpoints.py twice for a
bit, my bad.

Using update_profile_banner_image for the function name to update
profile banner image (that's what it was called previously)

.coveragerc

@@ -1,2 +1,8 @@
 [run]
 omit = twython/advisory.py
+
+[report]
+exclude_lines = 
+    pragma: no cover
+
+    def __repr__