added release date to v2.1.20
added release date to v2.1.20

ChrisTimperley/RepairBox,ChrisTimperley/AutomatedRepairBenchmarks.c,ChrisTimperley/RepairBox,ChrisTimperley/AutomatedRepairBenchmarks.c,ChrisTimperley/AutomatedRepairBenchmarks.c,ChrisTimperley/RepairBox,ChrisTimperley/RepairBox,ChrisTimperley/AutomatedRepairBenchmarks.c,ChrisTimperley/RepairBox,ChrisTimperley/RepairBox,ChrisTimperley/RepairBox,squaresLab/RepairBox,ChrisTimperley/AutomatedRepairBenchmarks.c,ChrisTimperley/RepairBox,ChrisTimperley/RepairBox,ChrisTimperley/AutomatedRepairBenchmarks.c,ChrisTimperley/AutomatedRepairBenchmarks.c,ChrisTimperley/RepairBox,ChrisTimperley/AutomatedRepairBenchmarks.c,ChrisTimperley/AutomatedRepairBenchmarks.c