Rename work dates to planned dates

spec/dayoff_spec.cr

@@ -2,7 +2,7 @@ require "./spec_helper"
 
 describe Dayoff do
   it "can calc work hours" do
-    app = Dayoff::App.new("./spec/data/work-dates.json")
+    app = Dayoff::App.new("./spec/data/planned-dates.json")
     app.get_work_hours.should eq 20
   end
 end