Make bugbear slightly more polite (#298)

* make bugbear slightly more polite

Bugbear is great at catching bugs in our code, but can come across a bit rude when commenting on pull requests 😂  Obviously it's a robot, but we like to encourage polite discourse

* Update bugbear.py

Co-authored-by: Cooper Lees <me@cooperlees.com>

Co-authored-by: Cooper Lees <me@cooperlees.com>

bugbear.py

@@ -1192,8 +1192,8 @@ def visit_Lambda(self, node):
 }
 B015 = Error(
     message=(
-        "B015 Pointless comparison. This comparison does nothing but waste "
-        "CPU instructions. Either prepend `assert` or remove it."
+        "B015 Result of comparison is not used. This line doesn't do"
+        "anything. Did you intend to prepend it with assert?"
     )
 )
 B016 = Error(
@@ -1213,7 +1213,8 @@ def visit_Lambda(self, node):
 )
 B018 = Error(
     message=(
-        "B018 Found useless expression. Either assign it to a variable or remove it."
+        "B018 Found useless expression. Consider either assigning it to a "
+        "variable or removing it."
     )
 )
 B019 = Error(