Tweak small things in the cowboy manual

doc/src/manual/cowboy.asciidoc

@@ -26,10 +26,10 @@ fields() :: [Name
            | {Name, Constraints}
            | {Name, Constraints, Default}]
 
-Name :: atom()
+Name        :: atom()
 Constraints :: Constraint | [Constraint]
-Constraint :: cowboy_constraints:constraint()
-Default :: any()
+Constraint  :: cowboy_constraints:constraint()
+Default     :: any()
 ----
 
 Fields description for match operations.

doc/src/manual/cowboy.set_env.asciidoc

@@ -42,7 +42,7 @@ and `middlewares`.
 Value::
 
 The new value.
-
++
 The type of the value differs depending on the key.
 
 == Return value