Last slash in url should be ignored if present

When you mount engine in Rails its root_path has trailing slash. But inclusive is_active_link? enforces additional slash after url, so it results in double slash requirement.

E.g. when we are mounting Forem engine to "/forum" path
``` 
forem.root_path # => "/forum/"

request.fullpath = "/forum/"
is_active_link?(forem.root_path) # => true, GOOD

request.fullpath = "/forum/mytopic"
is_active_link?(forem.root_path) # => false, BAD

request.fullpath = "/forum//mytopic"
is_active_link?(forem.root_path) # => true, BAD