remove unused values from default request params

Recently, the Fitbit API appears to throw bad request errors
if passing empty params to some of its endpoints - in particular
it would error out on the activity logs list endpoint as both the
beforeDate and afterDate params are being sent over, even though
the afterDate param is null by default. Previously, it looks like
Fitbit's API would gracefully handle these nil params but in this
case it explicitly fails as you can't have both a before and after
date set at the same time.

This updates affected methods so that unused values are removed
from the default params object. There should be no difference in
behavior other than fixing the recently broken activity logs
endpoint.

lib/fitbit_api/activities.rb

@@ -61,7 +61,7 @@ def all_activities
     # @option params :limit [Integer] The max of the number of entries returned (max: 20)
 
     def activity_logs_list(params = {})
-      default_params = { before_date: Date.today, after_date: nil, sort: 'desc', limit: 20, offset: 0 }
+      default_params = { before_date: Date.today, sort: 'desc', limit: 20, offset: 0 }
       get("user/#{user_id}/activities/list.json", default_params.merge(params))
     end
 

lib/fitbit_api/electrocardiogram.rb

@@ -16,7 +16,7 @@ class Client
     # @option params :limit [Integer] The max of the number of entries returned (max: 10)
 
     def ecg_logs_list(params = {})
-      default_params = { before_date: Date.today, after_date: nil, sort: 'desc', limit: 10, offset: 0 }
+      default_params = { before_date: Date.today, sort: 'desc', limit: 10, offset: 0 }
       get("user/#{user_id}/ecg/list.json", default_params.merge(params))
     end
   end

lib/fitbit_api/sleep.rb

@@ -50,7 +50,7 @@ def sleep_logs_by_date_range(opts = {})
     # @option params :limit [Integer] The max of the number of entries returned (max: 100)
 
     def sleep_logs_list(params = {})
-      default_params = { before_date: Date.today, after_date: nil, sort: 'desc', limit: 20, offset: 0 }
+      default_params = { before_date: Date.today, sort: 'desc', limit: 20, offset: 0 }
       get("user/#{user_id}/sleep/list.json", default_params.merge(params))
     end