changed column names in report

reports/spark_question1_global_change_last_15.csv

-,yearID,birthCountry,countNum2016,yearID,birthCountry,countNum2001,diff,percentChange
+,yearID,country2016,countNum2016,yearID,country2001,countNum2001,diff,percentChange
 0,2016,Germany,4,2001,Germany,1,3,300.0
 1,2016,D.R.,134,2001,D.R.,109,25,22.93577981651376
 2,2016,Nicaragua,3,2001,Nicaragua,2,1,50.0